drm/virtio: Remove return from void function

This patch fixes the checkpatch.pl warning:

virtgpu_ttm.c:181: WARNING: void function return statements are not
generally useful
...
Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/fd8dc6599c81c7aec6753c8552c1cabb7baa7577.1519343668.git.rodrigosiqueiramelo@gmail.comSigned-off-by: Gerd Hoffmann <kraxel@redhat.com>

drivers/gpu/drm/virtio/virtgpu_ttm.c

@@ -177,7 +177,6 @@ static void ttm_bo_man_put_node(struct ttm_mem_type_manager *man,
 				struct ttm_mem_reg *mem)
 {
 	mem->mm_node = (void *)NULL;
-	return;
 }
 
 static int ttm_bo_man_init(struct ttm_mem_type_manager *man,
@@ -244,7 +243,6 @@ static void virtio_gpu_evict_flags(struct ttm_buffer_object *bo,
 	placement->busy_placement = &placements;
 	placement->num_placement = 1;
 	placement->num_busy_placement = 1;
-	return;
 }
 
 static int virtio_gpu_verify_access(struct ttm_buffer_object *bo,