Input: gpio_keys_polled - request GPIO pin as input.

GPIOF_IN flag was lost in:
Commit 633a21d8

("input: gpio_keys_polled: Add support for GPIO
descriptors").

Without this flag, legacy code path (for non-descriptor GPIO declarations)
would configure GPIO as output (0 meaning GPIOF_DIR_OUT | GPIOF_INIT_LOW).

Cc: stable@vger.kernel.org
Signed-off-by: Vincent Pelletier <plr.vincent@gmail.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>