The event mask was specified as 0xF (4 bits) when in reality is 0x1F (5
bits) in order to be capable of representing all FIFO length values from
0 to 16.

This caused a problem: when the keypad reported 16 pending events the
driver took it as 0, and did nothing. This in turn caused the keypad to
re-issue the interrupt over and over again.
Signed-off-by: NGuido Martínez <guido@vanguardiasur.com.ar>
Acked-by: NMichael Hennerich <michael.hennerich@analog.com>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>