usb: gadget: composite: Return bcdUSB 0x0310

The USB 3.1 specification replaces the USB 3.0 specification and all new
devices that are running at SuperSpeed or higher speeds must report a
bcdUSB of 0x0310.

Refer to USB 3.1 Specification, Revision 1.0, Section 9.6.

Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>