Fix Cycles map range node missing clamp socket

No effect on the Blender integration yet, but needs to be solved for the
upcoming change to encapsulate sockets.

intern/cycles/render/nodes.cpp

@@ -5756,6 +5756,7 @@ NODE_DEFINE(MapRangeNode)
   SOCKET_IN_FLOAT(to_min, "To Min", 0.0f);
   SOCKET_IN_FLOAT(to_max, "To Max", 1.0f);
   SOCKET_IN_FLOAT(steps, "Steps", 4.0f);
+  SOCKET_IN_BOOLEAN(clamp, "Clamp", false);
 
   SOCKET_OUT_FLOAT(result, "Result");