Input: tc3589x-keypad - fix keymap size

The keymap size used by tc3589x is too low, leading to the driver
overwriting other people's memory.  Fix this by making the driver
use the automatically allocated keymap provided by
matrix_keypad_build_keymap() instead of allocating one on its own.

Signed-off-by: Rabin Vincent <rabin.vincent@stericsson.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>