irda: use msecs_to_jiffies() rather than manual calculation

Also use mod_timer() instead of direct assignment to "expires".
Signed-off-by: NXi Wang <xi.wang@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/irda/af_irda.c

@@ -2558,8 +2558,8 @@ static int irda_getsockopt(struct socket *sock, int level, int optname,
 			self->errno = 0;
 			setup_timer(&self->watchdog, irda_discovery_timeout,
 					(unsigned long)self);
-			self->watchdog.expires = jiffies + (val * HZ/1000);
-			add_timer(&(self->watchdog));
+			mod_timer(&self->watchdog,
+				  jiffies + msecs_to_jiffies(val));
 
 			/* Wait for IR-LMP to call us back */
 			__wait_event_interruptible(self->query_wait,