usb: gadget: printer: add container_of helper for printer_dev

5 uses of container_of() in the same context justify wrapping it
in a static inline function.

Signed-off-by: Andrzej Pietrasiewicz <[e-mail]>
Signed-off-by: Felipe Balbi <[e-mail]>

drivers/usb/gadget/legacy/printer.c

···
 	struct usb_function	function;
 };
 
+static inline struct printer_dev *func_to_printer(struct usb_function *f)
+{
+	return container_of(f, struct printer_dev, function);
+}
+
 static struct printer_dev usb_printer_gadget;
 
 /*-------------------------------------------------------------------------*/
···
 static int printer_func_setup(struct usb_function *f,
 		const struct usb_ctrlrequest *ctrl)
 {
-	struct printer_dev *dev = container_of(f, struct printer_dev, function);
+	struct printer_dev *dev = func_to_printer(f);
 	struct usb_composite_dev *cdev = f->config->cdev;
 	struct usb_request	*req = cdev->req;
 	int			value = -EOPNOTSUPP;
···
 		struct usb_function *f)
 {
 	struct usb_gadget *gadget = c->cdev->gadget;
-	struct printer_dev *dev = container_of(f, struct printer_dev, function);
+	struct printer_dev *dev = func_to_printer(f);
 	struct device *pdev;
 	struct usb_composite_dev *cdev = c->cdev;
 	struct usb_ep *in_ep;
···
 	struct printer_dev	*dev;
 	struct usb_request	*req;
 
-	dev = container_of(f, struct printer_dev, function);
+	dev = func_to_printer(f);
 
 	device_destroy(usb_gadget_class, g_printer_devno);
 
···
 static int printer_func_set_alt(struct usb_function *f,
 		unsigned intf, unsigned alt)
 {
-	struct printer_dev *dev = container_of(f, struct printer_dev, function);
+	struct printer_dev *dev = func_to_printer(f);
 	int ret = -ENOTSUPP;
 
 	if (!alt)
···
 
 static void printer_func_disable(struct usb_function *f)
 {
-	struct printer_dev *dev = container_of(f, struct printer_dev, function);
+	struct printer_dev *dev = func_to_printer(f);
 	unsigned long		flags;
 
 	DBG(dev, "%s\n", __func__);