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/webcam.c b/drivers/usb/gadget/webcam.c
index d946f19..2a617c3 100644
--- a/drivers/usb/gadget/webcam.c
+++ b/drivers/usb/gadget/webcam.c
@@ -395,13 +395,14 @@
 	.dev		= &webcam_device_descriptor,
 	.strings	= webcam_device_strings,
 	.max_speed	= USB_SPEED_SUPER,
+	.bind		= webcam_bind,
 	.unbind		= webcam_unbind,
 };
 
 static int __init
 webcam_init(void)
 {
-	return usb_composite_probe(&webcam_driver, webcam_bind);
+	return usb_composite_probe(&webcam_driver);
 }
 
 static void __exit