src/drivers: Remove a trailing whitespace

Change-Id: If357da5d84a255e0bdf8784d559ee0941045bbd6
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: http://review.coreboot.org/6309
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>