gssd: use correct test for success of getrlimit()

commit 7c5cb5e732a4b8704f8c79ec819c5d271e040339
    gssd: base the size of the fd array on the RLIMIT_NOFILE limit.

didn't actually work as claimed.  It only uses the returned value
if getrlimit() returns -1  -- which of course it only does when
there was an error.

So change the test to "== 0".

Reported-by: Leonardo Chiquitto< lchiquitto@suse.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Steve Dickson <steved@redhat.com>