There were a few build warnings in the USB driver to clean
up before -Werror may be enabled.
Change-Id: I220cfcf0ee926912a184a91d3ced3ba61259130e
Signed-off-by: Marc Jones <marc.jones@se-eng.com>
Reviewed-on: http://review.coreboot.org/7921
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>