FoxESS (Modbus): heartbeat: use ensureReg for setpoint writes

Some firmware rejects WriteMultipleRegisters (FC 0x10) with exception 3
when the register already holds the value being written. Use ensureReg
in the heartbeat so it skips the write when the setpoint is unchanged,
avoiding spurious error logs every 30s.

Author: GurliGebis

charger/foxess-modbus.go

@@ -218,9 +218,9 @@ func (wb *FoxESSEVC) heartbeat(ctx context.Context) {
 			_, err = wb.conn.WriteSingleRegister(foxRegChargingControl, foxChargingStop)
 		} else if cur != 0 {
 			if pbox {
-				err = wb.writeReg(foxRegMaxCurrent, cur)
+				err = wb.ensureReg(foxRegMaxCurrent, cur)
 			} else {
-				err = wb.writeReg(foxRegMaxPower, cur)
+				err = wb.ensureReg(foxRegMaxPower, cur)
 			}
 		}
 		if err != nil {