Fixes the following warnings from sparse:
	drivers/iio/adc/ad7266.c:140:16: warning: cast to restricted __be16
	drivers/iio/adc/ad7266.c:140:16: warning: cast to restricted __be16
	drivers/iio/adc/ad7266.c:140:16: warning: cast to restricted __be16
	drivers/iio/adc/ad7266.c:140:16: warning: cast to restricted __be16
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>