staging:iio:resolver:ad2s1210 fix negative IIO_ANGL_VEL read

gcc-7 points out an older regression:

drivers/staging/iio/resolver/ad2s1210.c: In function 'ad2s1210_read_raw':
drivers/staging/iio/resolver/ad2s1210.c:515:42: error: '<<' in boolean context, did you mean '<' ? [-Werror=int-in-bool-context]

The original code had 'unsigned short' here, but incorrectly got
converted to 'bool'. This reverts the regression and uses a normal
type instead.

Fixes: 29148543 ("staging:iio:resolver:ad2s1210 minimal chan spec conversion.")
Cc: stable@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>