printer gadget: BKL pushdown

Add explicit lock_kernel() calls to printer_open()
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

drivers/usb/gadget/printer.c

@@ -462,6 +462,7 @@ printer_open(struct inode *inode, struct file *fd)
 	unsigned long		flags;
 	int			ret = -EBUSY;
 
+	lock_kernel();
 	dev = container_of(inode->i_cdev, struct printer_dev, printer_cdev);
 
 	spin_lock_irqsave(&dev->lock, flags);
@@ -477,7 +478,7 @@ printer_open(struct inode *inode, struct file *fd)
 	spin_unlock_irqrestore(&dev->lock, flags);
 
 	DBG(dev, "printer_open returned %x\n", ret);
-
+	unlock_kernel();
 	return ret;
 }