Input: tc3589x-keypad - remove unnecessary checks

settle_time and debounce_period are u8 and thus can not be greater than
TC3589x_MAX_DEBOUNCE_SETTLE which is 255.

There also no need to mask out nibbles form board->krow and board->kcol
as we validate that they are in correct range.

Reported-by: Werner <w.landgraf@ru.ru>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>