`genbuild_h.sh` checks whether it is running from a coreboot's own git
worktree to decide whether to use git as the time source. This check
fails when `${top}/.git` is a gitfile, e.g. when coreboot is a
submodule.
Add a proper `git rev-parse` call to check the condition, remove `$top`
which is not used anymore.
Change-Id: I8bb13d607a01f4f28fa8b165769e0a1f702da362
Signed-off-by: Alex Thiessen <alex.thiessen.de+coreboot@gmail.com>
Reviewed-on: https://review.coreboot.org/23256
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
1758fd2a32