drm/vgem: Set unique to "vgem"

Since there's only one global instance ever we don't need to have
anything fancy. Stops a WARNING in the get_unique ioctl that the
unique name isn't set.

Cc: <stable@vger.kernel.org> # 4.1+ only
Reportedy-and-tested-by: Fabio Coatti <fabio.coatti@gmail.com>
Cc: Fabio Coatti <fabio.coatti@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/vgem/vgem_drv.c

@@ -328,6 +328,8 @@ static int __init vgem_init(void)
 		goto out;
 	}
 
+	drm_dev_set_unique(vgem_device, "vgem");
+
 	ret  = drm_dev_register(vgem_device, 0);
 
 	if (ret)