Fix Build error 'parameter name omitted' in logind

Fixes #918 by adding the omitted parameter name in
active_sessions_count().

Signed-off-by: Pablo Saavedra <psaavedra@igalia.com>

lib/logind.c

@@ -36,7 +36,7 @@ done:
     return ret;
 }
 
-unsigned long active_sessions_count(const char *name, unsigned long unused)
+unsigned long active_sessions_count(const char *name, unsigned long unused(limit))
 {
     struct passwd *pw;
     unsigned long count = 0;