cuse: fix memory leak

The problem is that fuse_dev_alloc() acquires an extra reference to cc.fc,
and the original ref count is never dropped.

Reported-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Fixes: cc080e9e9be1 ("fuse: introduce per-instance fuse_dev structure")
Cc: <stable@vger.kernel.org> # v4.2+

fs/fuse/cuse.c

@@ -549,6 +549,8 @@ static int cuse_channel_release(struct inode *inode, struct file *file)
 		unregister_chrdev_region(cc->cdev->dev, 1);
 		cdev_del(cc->cdev);
 	}
+	/* Base reference is now owned by "fud" */
+	fuse_conn_put(&cc->fc);
 
 	rc = fuse_dev_release(inode, file);	/* puts the base reference */