Fix REPO, BRANCH and HASH variables

ci_check incorrectly builds the Makefile variables for cloning the RTL repo in the case where the user wants to override what's in /<core>/sim/Common.mk. I stumbled across this one while testing 576. The fix is trivial.

This is something we'll want to propagate the dev branch for all cores. I'm deliberately pushing this onto the master, as it gives us an opportunity to see how that will work.

Signed-off-by: MikeOpenHWGroup mike@openhwgroup.org