[media] lirc_dev: avoid double mutex unlock

We can only unlock if mutex_lock() succeeds.

Fixes the following warning:
	drivers/media/rc/lirc_dev.c:535 lirc_dev_fop_close() error: double unlock 'mutex:&lirc_dev_lock'
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/rc/lirc_dev.c

@@ -506,6 +506,7 @@ int lirc_dev_fop_close(struct inode *inode, struct file *file)
 {
 	struct irctl *ir = irctls[iminor(inode)];
 	struct cdev *cdev;
+	int ret;
 
 	if (!ir) {
 		printk(KERN_ERR "%s: called with invalid irctl\n", __func__);
@@ -516,7 +517,8 @@ int lirc_dev_fop_close(struct inode *inode, struct file *file)
 
 	dev_dbg(ir->d.dev, LOGHEAD "close called\n", ir->d.name, ir->d.minor);
 
-	WARN_ON(mutex_lock_killable(&lirc_dev_lock));
+	ret = mutex_lock_killable(&lirc_dev_lock);
+	WARN_ON(ret);
 
 	rc_close(ir->d.rdev);
 
@@ -532,6 +534,7 @@ int lirc_dev_fop_close(struct inode *inode, struct file *file)
 		kfree(ir);
 	}
 
+	if (!ret)
 		mutex_unlock(&lirc_dev_lock);
 
 	return 0;