If refspec is pointing to an upstream branch name, the checkout for a
second run will not reset a repo back to the upstream commit. That is
because we applied the repo patches to a local branch that carries the
name of the upstream one.
Fix that by switching to local branch prior to applying any patches.
Reported-by: Belisko Marek <marek.belisko@gmail.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>