tun: fix misleading comment format

The comment above tun_flow_save_rps_rxhash() starts with "/**" which
makes it look like kerneldoc comment and results in warnings when
building with W=1. Fix the format to make it look like a normal comment.
Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -546,8 +546,7 @@ static void tun_flow_update(struct tun_struct *tun, u32 rxhash,
 	rcu_read_unlock();
 }
 
-/**
- * Save the hash received in the stack receive path and update the
+/* Save the hash received in the stack receive path and update the
  * flow_hash table accordingly.
  */
 static inline void tun_flow_save_rps_rxhash(struct tun_flow_entry *e, u32 hash)