drm/virtio: simplify the return expression

Simplify the return expression.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Minghao Chi <chi.minghao@zte.com.cn>
Link: http://patchwork.freedesktop.org/patch/msgid/20220429054911.3851977-1-chi.minghao@zte.com.cn


Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>