Add multiplier to RPM sensor (Fix #1688), fix offset/ratio DSBs

radio/src/telemetry/frsky_sport.cpp

@@ -259,6 +259,7 @@ void frskySportSetDefault(int index, uint16_t id, uint8_t instance)
     }
     if (unit == UNIT_RPMS) {
       telemetrySensor.custom.ratio = 1;
+      telemetrySensor.custom.offset = 1;
     }
   }
   else {

radio/src/telemetry/telemetry.cpp

@@ -172,7 +172,7 @@ void TelemetryItem::setValue(const TelemetrySensor & sensor, int32_t val, uint32
     newVal = 0;
   }
   else if (unit == UNIT_RPMS) {
-    newVal = newVal / sensor.custom.ratio;
+    newVal = (newVal * sensor.custom.offset) / sensor.custom.ratio;
   }
   else {
     newVal = sensor.getValue(newVal, unit, prec);