usb: gadget: udc: remove unused 'driver_desc'

Fix the following gcc warning:

drivers/usb/gadget/udc/gr_udc.c:51:19: warning: ‘driver_desc’ defined
but not used [-Wunused-const-variable=]
 static const char driver_desc[] = DRIVER_DESC;
                   ^~~~~~~~~~~
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

drivers/usb/gadget/udc/gr_udc.c

@@ -48,7 +48,6 @@
 #define	DRIVER_DESC	"Aeroflex Gaisler GRUSBDC USB Peripheral Controller"
 
 static const char driver_name[] = DRIVER_NAME;
-static const char driver_desc[] = DRIVER_DESC;
 
 #define gr_read32(x) (ioread32be((x)))
 #define gr_write32(x, v) (iowrite32be((v), (x)))