Set GPIOKPF_DEBOUNCE, just in case

This flag is already set by Motorola, as it is included in
GPIOKPF_REMOVE_PHANTOM_KEYS. I assume that nobody at Motorola
looked at this flag, as they would have seen that it also enable
the debouncing code which needs to have a debounce_delay set.
When the delay is 0 and the code is active, the bouncing even gets
worse, as the keypad is scanned more rapidly