vfio/platform: fix module_put call in error flow

The ->parent_module is the one that use in try_module_get. It should
also be the one the we use in module_put during vfio_platform_open().

Fixes: 32a2d71 ("vfio: platform: introduce vfio-platform-base module")
Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Message-Id: <20210518192133.59195-1-mgurtovoy@nvidia.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/platform/vfio_platform_common.c

@@ -291,7 +291,7 @@ static int vfio_platform_open(struct vfio_device *core_vdev)
 	vfio_platform_regions_cleanup(vdev);
 err_reg:
 	mutex_unlock(&driver_lock);
-	module_put(THIS_MODULE);
+	module_put(vdev->parent_module);
 	return ret;
 }