rfkill: gpio: fix memory leak in probe error path

Make sure to free the rfkill device in case registration fails during
probe.

Fixes: 5e7ca393 ("net: rfkill: gpio: convert to resource managed allocation")
Cc: stable <stable@vger.kernel.org>	# 3.13
Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>