md: remove clumsy usage of do_sync_mapping_range from bitmap code

and replace with vfs_fsync which is much neater (but wasn't exported,
or even in existence at the time the code was written).

Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/bitmap.c

@@ -1624,10 +1624,11 @@ int bitmap_create(mddev_t *mddev)
 	bitmap->offset = mddev->bitmap_offset;
 	if (file) {
 		get_file(file);
-		do_sync_mapping_range(file->f_mapping, 0, LLONG_MAX,
-				      SYNC_FILE_RANGE_WAIT_BEFORE |
-				      SYNC_FILE_RANGE_WRITE |
-				      SYNC_FILE_RANGE_WAIT_AFTER);
+		/* As future accesses to this file will use bmap,
+		 * and bypass the page cache, we must sync the file
+		 * first.
+		 */
+		vfs_fsync(file, file->f_dentry, 1);
 	}
 	/* read superblock from bitmap file (this sets bitmap->chunksize) */
 	err = bitmap_read_sb(bitmap);