Input: omap-keypad - fix error handling code

According to the previous error handling code, it is likely that 'goto
err_free_keymap' is expected here in order to avoid a memory leak in error
handling path.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>