Initialize OAIgraph before usage

Newer GCC releases warn about the scope being uninitialized:

openair1/PHY/TOOLS/nr_phy_scope.c:1076:20: error: ‘graph.text’ is used uninitialized [-Werror=uninitialized]

This is correct, as we don't initialize the scope. This commit correctly
initializes the scope.

openair1/PHY/TOOLS/nr_phy_scope.c

@@ -193,7 +193,9 @@ void websrv_setpoint(int x, int y, websrv_scopedata_msg_t *msg)
   msg->data_xy[msg->data_xy[0]] = (int16_t)y;
 }
 #endif
-static void commonGraph(OAIgraph_t *graph, int type, FL_Coord x, FL_Coord y, FL_Coord w, FL_Coord h, const char *label, FL_COLOR pointColor) {
+static void commonGraph(OAIgraph_t *graph, int type, FL_Coord x, FL_Coord y, FL_Coord w, FL_Coord h, const char *label, FL_COLOR pointColor)
+{
+  memset(graph, 0, sizeof(*graph));
   if (type==WATERFALL) {
     graph->waterFallh=h-15;
     graph->waterFallAvg=malloc(sizeof(*graph->waterFallAvg) * graph->waterFallh);