writeback: remove writeback_inodes_wbc

This was just an odd wrapper around writeback_inodes_wb.  Removing this
also allows to get rid of the bdi member of struct writeback_control
which was rather out of place there.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 660a87a..6e0b09a 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -340,14 +340,13 @@
 static void bdi_flush_io(struct backing_dev_info *bdi)
 {
 	struct writeback_control wbc = {
-		.bdi			= bdi,
 		.sync_mode		= WB_SYNC_NONE,
 		.older_than_this	= NULL,
 		.range_cyclic		= 1,
 		.nr_to_write		= 1024,
 	};
 
-	writeback_inodes_wbc(&wbc);
+	writeback_inodes_wb(&bdi->wb, &wbc);
 }
 
 /*
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 54f28bd..37498ef 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -495,7 +495,6 @@
 
 	for (;;) {
 		struct writeback_control wbc = {
-			.bdi		= bdi,
 			.sync_mode	= WB_SYNC_NONE,
 			.older_than_this = NULL,
 			.nr_to_write	= write_chunk,
@@ -537,7 +536,7 @@
 		 * up.
 		 */
 		if (bdi_nr_reclaimable > bdi_thresh) {
-			writeback_inodes_wbc(&wbc);
+			writeback_inodes_wb(&bdi->wb, &wbc);
 			pages_written += write_chunk - wbc.nr_to_write;
 			get_dirty_limits(&background_thresh, &dirty_thresh,
 				       &bdi_thresh, bdi);