fs/9p: Remove unused extern declaration

commit bd238fb4 ("9p: Reorganization of 9p file system code")
left behind this.
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com>
Signed-off-by: Eric Van Hensbergen <ericvh@kernel.org>

fs/9p/v9fs.c

@@ -545,8 +545,6 @@ void v9fs_session_begin_cancel(struct v9fs_session_info *v9ses)
 	p9_client_begin_disconnect(v9ses->clnt);
 }
 
-extern int v9fs_error_init(void);
-
 static struct kobject *v9fs_kobj;
 
 #ifdef CONFIG_9P_FSCACHE