cgit: fix Atom feed hostname from localhost to cgit.osmocom.org
Before:
$ curl -s https://cgit.osmocom.org/libosmocore/ | grep "Atom feed"
<link rel='alternate' title='Atom feed' href='http://localhost/libosmocore/atom/?h=master' type='application/atom+xml'/>
After:
$ curl -s https://cgit.osmocom.org/libosmocore/ | grep "Atom feed"
<link rel='alternate' title='Atom feed' href='http://cgit.osmocom.org/libosmocore/atom/?h=master' type='application/atom+xml'/>
Change-Id: Iaab14e254acc0356f0d3639924e3b6b528d57973
