Input: twl40300-keypad - fix handling of "all ground" rows

The Nokia RX51 board code (arch/arm/mach-omap2/board-rx51-peripherals.c)
defines a key map for the matrix keypad keyboard. The hardware seems to
use all of the 8 rows and 8 columns of the keypad, although not all
possible locations are used.

The TWL4030 supports keypads with at most 8 rows and 8 columns. Most keys
are defined with a row and column number between 0 and 7, except

        KEY(0xff, 2, KEY_F9),
        KEY(0xff, 4, KEY_F10),
        KEY(0xff, 5, KEY_F11),

which represent keycodes that should be emitted when entire row is
connected to the ground.  since the driver handles this case as if we
had an extra column in the key matrix. Unfortunately we do not allocate
enough space and end up owerwriting some random memory.

Reported-and-tested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: stable@kernel.org
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>