writeback: Fix some comment errors

Signed-off-by: Wanpeng Li <liwp@linux.vnet.ibm.com>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 41a3ccf..0b2c87e 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -628,8 +628,8 @@
 		}
 
 		/*
-		 * Don't bother with new inodes or inodes beeing freed, first
-		 * kind does not need peridic writeout yet, and for the latter
+		 * Don't bother with new inodes or inodes being freed, first
+		 * kind does not need periodic writeout yet, and for the latter
 		 * kind writeout is handled by the freer.
 		 */
 		spin_lock(&inode->i_lock);