Fix cleaning SeaBIOS from coreboot makefile

Fix cleaning SeaBIOS from coreboot makefile

The coreboot makefile didn't pass the OUT and CC variables to seabios,
so the clean didn't clean anything.

Change-Id: Ieaf0c417d6e5dfb9e0a11df70b03d6313919578b
Signed-off-by: Marc Jones <marc.jones@se-eng.com>
Reviewed-on: http://review.coreboot.org/801
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martin@se-eng.com>
Reviewed-by: Marc Jones <marcj303@gmail.com>