variants: Heltec Mesh Solar: Use DC/DC regulator

The schematic shows the LC circuit for the internal DC/DC regulator
to be available. Enable it to save power.

Signed-off-by: Frieder Schrempf <frieder@fris.de>

variants/heltec_mesh_solar/MeshSolarBoard.h

@@ -20,7 +20,7 @@
 #define SX126X_DIO2_AS_RF_SWITCH  true
 #define SX126X_DIO3_TCXO_VOLTAGE   1.8
 
-class MeshSolarBoard : public NRF52BoardOTA {
+class MeshSolarBoard : public NRF52BoardDCDC, public NRF52BoardOTA {
 public:
   MeshSolarBoard() : NRF52BoardOTA("MESH_SOLAR_OTA") {}
   void begin();