Documentation: iio: make ADXL Y-axis calibbias description consistent

Documentation: iio: make ADXL Y-axis calibbias description consistent

The Y-axis calibbias rows in adxl345.rst, adxl313.rst and adxl380.rst
use a different wording than the matching X-axis and Z-axis rows in
the same tables: the X/Z rows say "Calibration offset for the
X/Z-axis accelerometer channel." while the Y row says "Y-axis (or
y-axis) acceleration offset correction".

Make the Y-axis row match the other two so each driver's sysfs
table has consistent capitalisation and wording.

Signed-off-by: Stepan Ionichev <sozdayvek@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>