iio: proximity: pulsedlight v2: Tidy up an endian issue

Sparse identified the following
CHECK   drivers/iio/proximity/pulsedlight-lidar-lite-v2.c
drivers/iio/proximity/pulsedlight-lidar-lite-v2.c:144:24: warning: cast to restricted __be16
drivers/iio/proximity/pulsedlight-lidar-lite-v2.c:144:24: warning: cast to restricted __be16
drivers/iio/proximity/pulsedlight-lidar-lite-v2.c:144:24: warning: cast to restricted __be16
drivers/iio/proximity/pulsedlight-lidar-lite-v2.c:144:24: warning: cast to restricted __be16

This cleans up by adding a local variable to hold the value whilst
it is __be16 before applying endian converstion into eventual destination.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Matt Ranostay <matt.ranostay@konsulko.com>