Input: matrix_keypad - avoid repeatedly converting GPIO to IRQ

There is no need to do conversion from GPIOs to interrupt numbers.
Convert row GPIOs to interrupt numbers once in probe() and use
this information when the driver needs to enable or disable given
interrupt line.

Link: https://lore.kernel.org/r/20240121053232.276968-1-dmitry.torokhov@gmail.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>