drm: Fix respecting custom mode refresh rates

This was being overwritten by some dynamic refresh code.

src/drm.cpp

@@ -493,6 +493,8 @@ static bool refresh_state( drm_t *drm )
 
 		conn->current.crtc_id = conn->initial_prop_values["CRTC_ID"];
 
+		conn->target_refresh = 0;
+
 		drm_log.debugf("found new connector '%s'", conn->name);
 	}
 
@@ -755,6 +757,8 @@ static bool setup_best_connector(struct drm_t *drm, bool force)
 		return false;
 	}
 
+	best->target_refresh = mode->vrefresh;
+
 	if (!drm_set_mode(drm, mode)) {
 		return false;
 	}
@@ -2280,6 +2284,9 @@ int drm_get_default_refresh(struct drm_t *drm)
 	if ( drm->preferred_refresh )
 		return drm->preferred_refresh;
 
+	if ( drm->connector && drm->connector->target_refresh )
+		return drm->connector->target_refresh;
+
 	if ( drm->connector && drm->connector->connector )
 	{
 		drmModeConnector *connector = drm->connector->connector;

src/drm.hpp

@@ -87,6 +87,8 @@ struct connector {
 	char *make;
 	char *model;
 
+	int target_refresh;
+
 	struct {
 		uint32_t crtc_id;
 	} current, pending;