iio: adc: ti-adc128s052: Simplify using be16_to_cpu()

The register data is 12-bit big-endian data. Use be16_to_cpu() to do
the conversion, and simple bitwise AND for masking to make it more
obvious.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://patch.msgid.link/8202060d90221beb9b8cf467606641349ad47fe9.1744022065.git.mazziesaccount@gmail.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>