gpio: mockup: fix resource leak in error path

commit 1b02d9e770cd7087f34c743f85ccf5ea8372b047 upstream.

If the module init function fails after creating the debugs directory,
it's never removed. Add proper cleanup calls to avoid this resource
leak.

Fixes: 9202ba23 ("gpio: mockup: implement event injecting over debugfs")
Cc: <stable@vger.kernel.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>