iio:chemical:atlas-ph-sensor: Fix use of 32 bit int to hold 16 bit big endian value

This will result in a random value being reported on big endian architectures.
(thanks to Lars-Peter Clausen for pointing out the effects of this bug)

Only effects a value printed to the log, but as this reports the settings of
the probe in question it may be of direct interest to users.

Also, fixes the following sparse endianness warnings:

drivers/iio/chemical/atlas-ph-sensor.c:215:9: warning: cast to restricted __be16
drivers/iio/chemical/atlas-ph-sensor.c:215:9: warning: cast to restricted __be16
drivers/iio/chemical/atlas-ph-sensor.c:215:9: warning: cast to restricted __be16
drivers/iio/chemical/atlas-ph-sensor.c:215:9: warning: cast to restricted __be16
drivers/iio/chemical/atlas-ph-sensor.c:215:9: warning: cast to restricted __be16
drivers/iio/chemical/atlas-ph-sensor.c:215:9: warning: cast to restricted __be16
drivers/iio/chemical/atlas-ph-sensor.c:215:9: warning: cast to restricted __be16
drivers/iio/chemical/atlas-ph-sensor.c:215:9: warning: cast to restricted __be16

Signed-off-by: Sandhya Bankar <bankarsandhya512@gmail.com>
Fixes: e8dd92bf ("iio: chemical: atlas-ph-sensor: add EC feature")
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>