fuse: use atomic64_t for khctr

...to get rid of one more fc->lock use.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/file.c

@@ -64,9 +64,7 @@ struct fuse_file *fuse_file_alloc(struct fuse_conn *fc)
 	RB_CLEAR_NODE(&ff->polled_node);
 	init_waitqueue_head(&ff->poll_wait);
 
-	spin_lock(&fc->lock);
-	ff->kh = ++fc->khctr;
-	spin_unlock(&fc->lock);
+	ff->kh = atomic64_inc_return(&fc->khctr);
 
 	return ff;
 }