usb: gadget: composite: Access SSP Dev Cap fields properly

Access multi-byte fields of the SSP Dev Cap descriptor using the correct
endianness.

Fixes: f228a8de ("usb: gadget: composite: Return SSP Dev Cap descriptor")
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>