usb: gadget: udc: mv_u3d_core: Remove unused static const 'driver_desc'

Looks like it's never been used.  Driver was mainlined in 2014.

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

 drivers/usb/gadget/udc/mv_u3d_core.c:35:19: warning: ‘driver_desc’ defined but not used [-Wunused-const-variable=]
 35 | static const char driver_desc[] = DRIVER_DESC;
 | ^~~~~~~~~~~

Cc: Felipe Balbi <balbi@kernel.org>
Cc: Jason Yan <yanaijie@huawei.com>
Cc: Yu Xu <yuxu@marvell.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200706133341.476881-23-lee.jones@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/udc/mv_u3d_core.c

@@ -32,7 +32,6 @@
 #define DRIVER_DESC		"Marvell PXA USB3.0 Device Controller driver"
 
 static const char driver_name[] = "mv_u3d";
-static const char driver_desc[] = DRIVER_DESC;
 
 static void mv_u3d_nuke(struct mv_u3d_ep *ep, int status);
 static void mv_u3d_stop_activity(struct mv_u3d *u3d,