usb: gadget: composite: Return bcdUSB 0x0310 for Superspeed and higher

As per USB 3.1 Specification, Revision 1.0, Section 9.6 all new
devices running at SuperSpeed or higher speeds must report a
bcdUSB of 0x0310.

Change-Id: I253d0114fadb33456c7a0eb823d29aade1f33dc1
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>