gpio: mxc: Unlock on error path in mxc_flip_edge()

gpio: mxc: Unlock on error path in mxc_flip_edge()

[ Upstream commit 37870358616ca7fdb1e90ad1cdd791655ec54414 ]

We recently added locking to this function but one error path was
over looked.  Drop the lock before returning.

Fixes: e5464277625c ("gpio: mxc: Protect GPIO irqchip RMW with bgpio spinlock")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Marek Vasut <marex@denx.de>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>