nfs: fix oops in nfs_rename()

Recent change is missing to update "rehash".  With that change, it will
become the cause of adding dentry to hash twice.

This explains the reason of Oops (dereference the freed dentry in
__d_lookup()) on my machine.

Signed-off-by: OGAWA Hirofumi <[email protected]>
Reported-by: Marvin <[email protected]>
Cc: Trond Myklebust <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Trond Myklebust <[email protected]>

fs/nfs/dir.c

@@ -1615,6 +1615,7 @@ static int nfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 				goto out;
 
 			new_dentry = dentry;
+			rehash = NULL;
 			new_inode = NULL;
 		}
 	}