media: stm32: dcmi: unregister notifier on probe failure

In the Linux kernel, the following vulnerability has been resolved: media: stm32: dcmi: unregister notifier on probe failure dcmi_graph_init() registers the async notifier before dcmi_probe() toggles the reset line. If reset_control_assert() or reset_control_deassert() fails afterwards, probe returns through err_cleanup and the driver core will not call dcmi_remove(). Unregister the notifier before cleaning it up on that error path, matching the successful remove path and the V4L2 async notifier lifetime rules. [hverkuil: added Fixes tag]