writeback: fix typo in the writeback_control comment

@@ -64,7 +64,7 @@ struct writeback_control {
 	long pages_skipped;		/* Pages which were not written */
 
 	/*
-	 * For a_ops->writepages(): is start or end are non-zero then this is
+	 * For a_ops->writepages(): if start or end are non-zero then this is
 	 * a hint that the filesystem need only write out the pages inside that
 	 * byterange.  The byte at `end' is included in the writeout request.
 	 */

@@ -1548,17 +1548,17 @@ int writeback_inodes_sb_if_idle(struct s
 		up_read(&sb->s_umount);
 		return 1;
 	} else
 		return 0;
 }
 EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
 
 /**
- * writeback_inodes_sb_if_idle	-	start writeback if none underway
+ * writeback_inodes_sb_nr_if_idle	-	start writeback if none underway
  * @sb: the superblock
  * @nr: the number of pages to write
  * @reason: reason why some writeback work was initiated
  *
  * Invoke writeback_inodes_sb if no writeback is currently underway.
  * Returns 1 if writeback was started, 0 if not.
  */
 int writeback_inodes_sb_nr_if_idle(struct super_block *sb,