buildroot

.gitlab-ci.yml: simplify (and fix) check-DEVELOPERS

The check-DEVELOPERS test would always fail, because && will return
the exit code of the left-hand side if not 0, so it *always* returns
1.

But in fact, the test can be simplified quite a lot: we can run
getdeveloper directly, without arguments. That should just print
'No action specified', but it will also print any syntax errors it
encountered. So we can just 'grep -v' the expected output away; if
there is anything more, grep will return 0, but if there is nothing
more, it will return 1. So we just need to invert the result.

Incidentally, this also fixes the incorrect remaining reference to
support/scripts.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>