9p: return on mutex_lock_interruptible()

If "err" is -EINTR here the original code calls mutex_unlock() and then
returns, but it should just return directly.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

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fs/9p/vfs_dir.c

@@ -130,6 +130,8 @@ static int v9fs_dir_readdir(struct file *filp, void *dirent, filldir_t filldir)
 	rdir = (struct p9_rdir *) fid->rdir;
 
 	err = mutex_lock_interruptible(&rdir->mutex);
+	if (err)
+		return err;
 	while (err == 0) {
 		if (rdir->tail == rdir->head) {
 			err = v9fs_file_readn(filp, rdir->buf, NULL,