gpio: pca953x: clarify log messages about auto increment feature

gpio: pca953x: clarify log messages about auto increment feature

The probe messages currently print "using AI" and "using no AI",
which can be confusing to users unfamiliar with the datasheet term.

Clarify these by spelling out "auto increment", which is the meaning
of the AI bit described in the register map.

No functional change, only clearer log wording and matching comment
update.

Signed-off-by: Michael Roth <mail@mroth.net>
Link: https://lore.kernel.org/r/20251018101404.3630905-1-mail@mroth.net
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>