drm/i915/gvt: return error when failing to take the module reference

When we fail to take the module reference, we go to the 'undo*' branch and
return. But the returned variable 'ret' has been set as zero by the
above code. Change 'ret' to '-ENODEV' in this situation.

Fixes: 9bdb073 ("drm/i915/gvt: Change KVMGT as self load module")
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1605187352-51761-1-git-send-email-wangxiongfeng2@huawei.com

Author: fenghusthu

drivers/gpu/drm/i915/gvt/kvmgt.c

@@ -829,8 +829,10 @@ static int intel_vgpu_open(struct mdev_device *mdev)
 	/* Take a module reference as mdev core doesn't take
 	 * a reference for vendor driver.
 	 */
-	if (!try_module_get(THIS_MODULE))
+	if (!try_module_get(THIS_MODULE)) {
+		ret = -ENODEV;
 		goto undo_group;
+	}
 
 	ret = kvmgt_guest_init(mdev);
 	if (ret)