fuse: Add missed unlock_page() to fuse_readpages_fill()

The above error path returns with page unlocked, so this place seems also
to behave the same.

Fixes: f8dbdf81 ("fuse: rework fuse_readpages()")
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/file.c

@@ -866,6 +866,7 @@ static int fuse_readpages_fill(void *_data, struct page *page)
 	}
 
 	if (WARN_ON(req->num_pages >= req->max_pages)) {
+		unlock_page(page);
 		fuse_put_request(fc, req);
 		return -EIO;
 	}