usb: dwc2-otg: remove unused variable

GCC 6.1 complains about this.

drivers/usb/gadget/dwc2_udc_otg.c:72:19: warning: 'driver_desc'
defined but not used [-Wunused-const-variable=]
 static const char driver_desc[] = DRIVER_DESC;
                   ^~~~~~~~~~~

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

drivers/usb/gadget/dwc2_udc_otg.c

@@ -63,13 +63,11 @@ static char *state_names[] = {
 	"WAIT_FOR_NULL_COMPLETE",
 };
 
-#define DRIVER_DESC "DWC2 HS USB OTG Device Driver, (c) Samsung Electronics"
 #define DRIVER_VERSION "15 March 2009"
 
 struct dwc2_udc	*the_controller;
 
 static const char driver_name[] = "dwc2-udc";
-static const char driver_desc[] = DRIVER_DESC;
 static const char ep0name[] = "ep0-control";
 
 /* Max packet size*/