Drop duplicate inclusion of src/vendorcode

Change-Id: I95908bdca51c5ee959ae9f2307d4b6e0e002d04a
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/857
Reviewed-by: Martin Roth <martin@se-eng.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Mathias Krause <minipli@googlemail.com>