virtio-gpu: fix shift wrapping bug in virtio_gpu_fence_event_create()

The ->ring_idx_mask variable is a u64 so static checkers, Smatch in
this case, complain if the BIT() is not also a u64.

drivers/gpu/drm/virtio/virtgpu_ioctl.c:50 virtio_gpu_fence_event_create()
warn: should '(1 << ring_idx)' be a 64 bit type?

Fixes: cd7f5ca3 ("drm/virtio: implement context init: add virtio_gpu_fence_event")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/YygN7jY0GdUSQSy0@kiliSigned-off-by: Gerd Hoffmann <kraxel@redhat.com>

drivers/gpu/drm/virtio/virtgpu_ioctl.c

@@ -47,7 +47,7 @@ static int virtio_gpu_fence_event_create(struct drm_device *dev,
 	struct virtio_gpu_fence_event *e = NULL;
 	int ret;
 
-	if (!(vfpriv->ring_idx_mask & (1 << ring_idx)))
+	if (!(vfpriv->ring_idx_mask & BIT_ULL(ring_idx)))
 		return 0;
 
 	e = kzalloc(sizeof(*e), GFP_KERNEL);