iio: accel: kxsd9: Replace "parent" with "dev"

What is passed to the .probe() and .remove() functions is
technically the parent of the created IIO device but it becomes
a big confusion for the head to have it named like this since
it is usually clear from context the "dev" refers to the physical
device, and when next adding PM callbacks a clean
"struct device *dev" pointer is passed to these and that makes
it even more confused. Rename "parent" to "dev" like in most
other drivers.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>