Corrected LCD only error

If only an LCD is defined and no menu or keyboard defined, there is a
compilation error.

Added conditional compilation.

Marlin/ultralcd.cpp

@@ -19,7 +19,10 @@ int absPreheatHotendTemp;
 int absPreheatHPBTemp;
 int absPreheatFanSpeed;
 
+#ifdef ULTIPANEL
 static float manual_feedrate[] = MANUAL_FEEDRATE;
+#endif // ULTIPANEL
+
 /* !Configuration settings */
 
 //Function pointer to menu functions.