OBS: latest: fix code path to add new package

Fix osmo_obs_add_rpm_spec() to not assume to be in the $oscdir.
This caused the following error when being called from
osmocom-latest-packages.sh in the code path for adding a new package:
  ls: cannot access 'osmo-gbproxy_*.tar.*': No such file or directory

Related: OS#5051
Change-Id: I467e332b69accfabba53332fdb9cd785991855fc

scripts/common-obs.sh

@@ -139,7 +139,7 @@ osmo_obs_add_rpm_spec() {
 	fi
 
 	# Set source file
-	tarball="$(ls -1 "${name}_"*".tar."*)"
+	tarball="$(cd "$oscdir" && ls -1 "${name}_"*".tar."*)"
 	sed -i "s/^Source:.*/Source:  $tarball/g" "$spec"
 
 	osc add "$spec"