Input: matrix_keypad - consolidate handling of clustered interrupt

Now that the driver stores interrupt numbers corresponding to individual
GPIOs in non-clustered mode, it is possible to unify handling of both
modes by storing clustered interrupt at position 0 and setting the
number of interrupts in this case to 1.

Link: https://lore.kernel.org/r/20240121053232.276968-2-dmitry.torokhov@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>