drm/virtio: fix an error code in virtio_gpu_init()

If devm_request_mem_region() fails this code currently returns success
but it should return -EBUSY.

Fixes: 6076a97 ("drm/virtio: implement blob resources: probe for host visible region")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: http://patchwork.freedesktop.org/patch/msgid/YBpy0GS7GfmafMfe@mwanda
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
(cherry picked from commit eb988a2)
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

drivers/gpu/drm/virtio/virtgpu_kms.c

@@ -163,6 +163,7 @@ int virtio_gpu_init(struct drm_device *dev)
 					     vgdev->host_visible_region.len,
 					     dev_name(&vgdev->vdev->dev))) {
 			DRM_ERROR("Could not reserve host visible region\n");
+			ret = -EBUSY;
 			goto err_vqs;
 		}