writeback: add bg_threshold parameter to __bdi_update_bandwidth()

No behavior change.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 2b8963f..ddb4652 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -143,6 +143,7 @@
 
 void __bdi_update_bandwidth(struct backing_dev_info *bdi,
 			    unsigned long thresh,
+			    unsigned long bg_thresh,
 			    unsigned long dirty,
 			    unsigned long bdi_thresh,
 			    unsigned long bdi_dirty,