arm: ep93xx: Don't try to release not acquired GPIO lines

Fail path of ep93xx_keypad_acquire_gpio() tries to release
GPIO lines not acquired successfully before. Fix this.

Signed-off-by: Rafal Prylowski <prylowski@metasoft.pl>
Acked-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Ryan Mallon <rmallon@gmail.com>