gpio: rcar: Remove checks for empty bankmasks

gpio: rcar: Remove checks for empty bankmasks

The GPIO core never passes empty bankmasks to the callbacks for handling
multiple signals at once.  Remove the superfluous checks, and refactor
the code.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/29fb200d3f92e79cdd5ce4048d2847c265f337b4.1750838486.git.geert+renesas@glider.be
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>