drivers:staging:iio: fix checkpatch complaint about space before comma

Fixes:
drivers/staging/iio/adc/ad7192.c:615: ERROR: space prohibited before that ','
drivers/staging/iio/meter/ade7759.c:119: ERROR: space prohibited before that ','

Signed-off-by: Zachary Warren <conflatulence@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>