drivers: iio: light: Fix sparse warnings

Fixing below warnings:

drivers/iio/light/max44000.c:217:18: warning: cast to restricted __be16
drivers/iio/light/max44000.c:217:18: warning: cast to restricted __be16
drivers/iio/light/max44000.c:217:18: warning: cast to restricted __be16
drivers/iio/light/max44000.c:217:18: warning: cast to restricted __be16

Signed-off-by: Sandhya Bankar <bankarsandhya512@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>