Remove the lock_kernel() call from chrdev_open()

All in-kernel char device open() functions now either have their own
lock_kernel() calls or clearly do not need one.
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

fs/char_dev.c

@@ -394,11 +394,8 @@ static int chrdev_open(struct inode *inode, struct file *filp)
 		cdev_put(p);
 		return -ENXIO;
 	}
-	if (filp->f_op->open) {
-		lock_kernel();
+	if (filp->f_op->open)
 		ret = filp->f_op->open(inode,filp);
-		unlock_kernel();
-	}
 	if (ret)
 		cdev_put(p);
 	return ret;