Fix early exit in modref_merge_call_site_flags

When adding support for static chain and return slot flags I forgot to update
early exit condition in modref_merge_call_site_flags.  This yields to wrong
code as demonstrated by the Fortran testcase attached to PR (which I hope
someone will help me to turn into testuite one).

gcc/ChangeLog:

2021-12-19  Jan Hubicka  <hubicka@ucw.cz>

	PR ipa/103766
	* ipa-modref.c (modref_merge_call_site_flags): Fix early exit condition