$ git clone -n https://src.fedoraproject.org/rpms/bcm283x-firmware.git /var/lib/mock/f39-build-1654287-40519/root/chroot_tmpdir/scmroot/bcm283x-firmware
Cloning into '/var/lib/mock/f39-build-1654287-40519/root/chroot_tmpdir/scmroot/bcm283x-firmware'...
$ git fetch origin c6d9fc5dc7be640f2f7d9f3b846b2c96ebecbbf1:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/bcm283x-firmware
 * [new ref]         c6d9fc5dc7be640f2f7d9f3b846b2c96ebecbbf1 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at c6d9fc5 Update to ce3a0b4