Update URL's to point to head rather than the deprecated
refs/heads/master.

Change-Id: I16f0c087762ff049115b67de3ac0b881aa4e4b40
Signed-off-by: Jon Murphy <jpmurphy@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/79785


Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Matt DeVillier <matt.devillier@amd.corp-partner.google.com>