staging:iio:ad9832: Mark transfer buffers as __be16

Fixes the following warnings from sparse:
	drivers/staging/iio/frequency/ad9832.c:43:26: warning: incorrect type in assignment (different base types)
	drivers/staging/iio/frequency/ad9832.c:43:26:    expected unsigned short [unsigned] [short] <noident>
	drivers/staging/iio/frequency/ad9832.c:43:26:    got restricted __be16 [usertype] <noident>
	drivers/staging/iio/frequency/ad9832.c:46:26: warning: incorrect type in assignment (different base types)
	drivers/staging/iio/frequency/ad9832.c:46:26:    expected unsigned short [unsigned] [short] <noident>
	drivers/staging/iio/frequency/ad9832.c:46:26:    got restricted __be16 [usertype] <noident>
	drivers/staging/iio/frequency/ad9832.c:49:26: warning: incorrect type in assignment (different base types)
	drivers/staging/iio/frequency/ad9832.c:49:26:    expected unsigned short [unsigned] [short] <noident>
	drivers/staging/iio/frequency/ad9832.c:49:26:    got restricted __be16 [usertype] <noident>
	drivers/staging/iio/frequency/ad9832.c:52:26: warning: incorrect type in assignment (different base types)
	drivers/staging/iio/frequency/ad9832.c:52:26:    expected unsigned short [unsigned] [short] <noident>
	drivers/staging/iio/frequency/ad9832.c:52:26:    got restricted __be16 [usertype] <noident>
	drivers/staging/iio/frequency/ad9832.c:65:27: warning: incorrect type in assignment (different base types)
	drivers/staging/iio/frequency/ad9832.c:65:27:    expected unsigned short [unsigned] [short] <noident>
	drivers/staging/iio/frequency/ad9832.c:65:27:    got restricted __be16 [usertype] <noident>
	drivers/staging/iio/frequency/ad9832.c:68:27: warning: incorrect type in assignment (different base types)
	drivers/staging/iio/frequency/ad9832.c:68:27:    expected unsigned short [unsigned] [short] <noident>
	drivers/staging/iio/frequency/ad9832.c:68:27:    got restricted __be16 [usertype] <noident>
	drivers/staging/iio/frequency/ad9832.c:107:26: warning: incorrect type in assignment (different base types)
	drivers/staging/iio/frequency/ad9832.c:107:26:    expected unsigned short [unsigned] data
	drivers/staging/iio/frequency/ad9832.c:107:26:    got restricted __be16 [usertype] <noident>
	drivers/staging/iio/frequency/ad9832.c:120:26: warning: incorrect type in assignment (different base types)
	drivers/staging/iio/frequency/ad9832.c:120:26:    expected unsigned short [unsigned] data
	drivers/staging/iio/frequency/ad9832.c:120:26:    got restricted __be16 [usertype] <noident>
	drivers/staging/iio/frequency/ad9832.c:133:26: warning: incorrect type in assignment (different base types)
	drivers/staging/iio/frequency/ad9832.c:133:26:    expected unsigned short [unsigned] data
	drivers/staging/iio/frequency/ad9832.c:133:26:    got restricted __be16 [usertype] <noident>
	drivers/staging/iio/frequency/ad9832.c:144:26: warning: incorrect type in assignment (different base types)
	drivers/staging/iio/frequency/ad9832.c:144:26:    expected unsigned short [unsigned] data
	drivers/staging/iio/frequency/ad9832.c:144:26:    got restricted __be16 [usertype] <noident>
	drivers/staging/iio/frequency/ad9832.c:277:18: warning: incorrect type in assignment (different base types)
	drivers/staging/iio/frequency/ad9832.c:277:18:    expected unsigned short [unsigned] data
	drivers/staging/iio/frequency/ad9832.c:277:18:    got restricted __be16 [usertype] <noident>

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>