usb: gadget: move bind() callback back to struct usb_composite_driver

This partly reverts 07a18bd7 ("usb gadget: don't save bind callback in
struct usb_composite_driver") and fixes new drivers. The section missmatch
problems was solved by whitelisting structs in question via __ref.

Cc: devel@driverdev.osuosl.org
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/gadget/printer.c b/drivers/usb/gadget/printer.c
index 0aab517..33c0c07 100644
--- a/drivers/usb/gadget/printer.c
+++ b/drivers/usb/gadget/printer.c
@@ -1274,6 +1274,7 @@
 	.dev            = &device_desc,
 	.strings        = dev_strings,
 	.max_speed      = USB_SPEED_HIGH,
+	.bind		= printer_bind,
 	.unbind		= printer_unbind,
 };
 
@@ -1297,7 +1298,7 @@
 		return status;
 	}
 
-	status = usb_composite_probe(&printer_driver, printer_bind);
+	status = usb_composite_probe(&printer_driver);
 	if (status) {
 		class_destroy(usb_gadget_class);
 		unregister_chrdev_region(g_printer_devno, 1);