Set the reserved fields of the SuperSpeed Plus Device Capability
descriptor to 0. Otherwise there might be stale data there which will
cause USB CV to fail.

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>