RCG: Add comment to dummy placeholder

src/fe/controllerIop.c

@@ -67,6 +67,8 @@ int getGpsTime( unsigned int* tsyncSec, unsigned int* tsyncUsec );
 #include "verify_slots.c"
 #include <drv/dac_info.c>
 #include <drv/adc_info.c>
+
+// dummy placeholder function that should never be called when there's no IOC
 int iop_dac_preload() {return 0;}
 #else
 #include "map.c"