autofs: use autofs4_free_ino() to kfree dentry data

kfree dentry data allocated by autofs4_new_ino() with autofs4_free_ino()
instead of raw kfree.  (since we have the interface to free autofs_info*)

This patch was modified to remove the need to set the dentry info field to
NULL dew to a change in the previous patch.

Link: http://lkml.kernel.org/r/20160812024805.12352.43650.stgit@pluto.themaw.net
Signed-off-by: Tomohiro Kusumi <kusumi.tomohiro@gmail.com>
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/autofs4/inode.c

@@ -340,7 +340,7 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent)
 	dput(root);
 	goto fail_free;
 fail_ino:
-	kfree(ino);
+	autofs4_free_ino(ino);
 fail_free:
 	kfree(sbi);
 	s->s_fs_info = NULL;