[make] Fix .idl submodule check

[3vilhamster]

What changed?
Updated the check of idls submodule for master since it was not working if you have out of date master or didn't pull it for a while.

Example failure:

cd idls
git checkout b25b18cb10b1d3880cbb7525811ce5f61a348758
make .idl-status

Error: Submodule commit b25b18cb10b1d3880cbb7525811ce5f61a348758 belongs to   origin/feature-dt-kind, not to master branch
make: *** [.idl-status] Error 1

Why?
The check was failing on fresh repo after git submodule update --init, since it does not fetch recent master.

How did you test it?
Checked on master and checked on the non-master commit.

Potential risks
CI fail, should be easy to rollback in case of issues.

Release notes

Documentation Changes

[Groxx]

I kinda wonder if git changed somewhere along the way, because I'm getting empty results from the current code...

... but eh. This looks better regardless, it was a moderate hack before and branch --contains (and --remote) seems like a clearly more reasonable check to do. Thanks!