usb: gadget: provide interface for legacy gadgets to get UDC name

Since commit 855ed04a3758b205e84b269f92d26ab36ed8e2f7 ("usb: gadget:
udc-core: independent registration of gadgets and gadget drivers") gadget
drivers can not assume that UDC drivers are already available on their
initialization. This broke the HACK, which was used in gadgetfs driver,
to get UDC controller name. This patch removes this hack and replaces it
by additional function in the UDC core (which is usefully only for legacy
drivers, please don't use it in the new code).

Reported-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>
diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
index 4252729..dd7c532 100644
--- a/include/linux/usb/gadget.h
+++ b/include/linux/usb/gadget.h
@@ -1136,6 +1136,7 @@
 		struct usb_gadget *gadget, void (*release)(struct device *dev));
 extern int usb_add_gadget_udc(struct device *parent, struct usb_gadget *gadget);
 extern void usb_del_gadget_udc(struct usb_gadget *gadget);
+extern char *usb_get_gadget_udc_name(void);
 
 /*-------------------------------------------------------------------------*/