ovl: fix comment typos

Fix two typos.
Reported-by: k2ci <kernel-bot@kylinos.cn>
Signed-off-by: Jiangshan Yi <yijiangshan@kylinos.cn>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/export.c

@@ -339,7 +339,7 @@ static struct dentry *ovl_obtain_alias(struct super_block *sb,
 	return dentry;
 }
 
-/* Get the upper or lower dentry in stach whose on layer @idx */
+/* Get the upper or lower dentry in stack whose on layer @idx */
 static struct dentry *ovl_dentry_real_at(struct dentry *dentry, int idx)
 {
 	struct ovl_entry *oe = dentry->d_fsdata;

fs/overlayfs/file.c

@@ -34,7 +34,7 @@ static char ovl_whatisit(struct inode *inode, struct inode *realinode)
 		return 'm';
 }
 
-/* No atime modificaton nor notify on underlying */
+/* No atime modification nor notify on underlying */
 #define OVL_OPEN_FLAGS (O_NOATIME | FMODE_NONOTIFY)
 
 static struct file *ovl_open_realfile(const struct file *file,