gpio: mockup: fix NULL pointer dereference when removing debugfs

In the Linux kernel, the following vulnerability has been resolved: gpio: mockup: fix NULL pointer dereference when removing debugfs We now remove the device's debugfs entries when unbinding the driver. This now causes a NULL-pointer dereference on module exit because the platform devices are unregistered *after* the global debugfs directory has been recursively removed. Fix it by unregistering the devices first.