usb: gadget: udc: mv_udc_core: Remove unused static const variable 'driver_desc'

Looks as though it's never been used.  Driver was introduced in 2014.

Fixes the following W=1 kernel build warning(s):

 drivers/usb/gadget/udc/mv_udc_core.c:56:19: warning: ‘driver_desc’ defined but not used [-Wunused-const-variable=]
 56 | static const char driver_desc[] = DRIVER_DESC;
 | ^~~~~~~~~~~

Cc: Felipe Balbi <balbi@kernel.org>
Cc: Chao Xie <chao.xie@marvell.com>
Cc: Neil Zhang <zhangwm@marvell.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200706133341.476881-15-lee.jones@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/udc/mv_udc_core.c

@@ -53,7 +53,6 @@
 static DECLARE_COMPLETION(release_done);
 
 static const char driver_name[] = "mv_udc";
-static const char driver_desc[] = DRIVER_DESC;
 
 static void nuke(struct mv_ep *ep, int status);
 static void stop_activity(struct mv_udc *udc, struct usb_gadget_driver *driver);