backends: Fix typo

Instead of checking all MetaMonitors in the monitor manager, we want to
look (as the function name says) in the MetaMonitors contained in the
given logical monitor.

Otherwise, it will return TRUE for every logical monitor, given we are
querying for an existing EDID.

https://bugzilla.gnome.org/show_bug.cgi?id=782032

src/backends/meta-input-settings.c

@@ -738,7 +738,7 @@ logical_monitor_has_monitor (MetaMonitorManager *monitor_manager,
   GList *monitors;
   GList *l;
 
-  monitors = meta_monitor_manager_get_monitors (monitor_manager);
+  monitors = meta_logical_monitor_get_monitors (logical_monitor);
   for (l = monitors; l; l = l->next)
     {
       MetaMonitor *monitor = l->data;