NFS: Fix a lock imbalance typo in nfs_access_cache_shrinker

Commit 9c7e7e2337 (NFS: Don't call iput() in
nfs_access_cache_shrinker) unintentionally removed the spin unlock for the
inode->i_lock.

Reported-by: David Howells <dhowells@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/dir.c

@@ -1741,6 +1741,7 @@ remove_lru_entry:
 			clear_bit(NFS_INO_ACL_LRU_SET, &nfsi->flags);
 			smp_mb__after_clear_bit();
 		}
+		spin_unlock(&inode->i_lock);
 	}
 	spin_unlock(&nfs_access_lru_lock);
 	nfs_access_free_list(&head);