[MATTER] fix TRV attr MinSetpointDeadBand shall allow 0-127 but ignore any attempted change

Author: kliffQorvo

src/app/clusters/thermostat-server/thermostat-server.cpp

@@ -720,6 +720,17 @@ CHIP_ERROR ThermostatAttrAccess::Write(const ConcreteDataAttributePath & aPath,
 
     switch (aPath.mAttributeId)
     {
+    case MinSetpointDeadBand::Id: {
+        int8_t minSetpointDeadBand;
+        ReturnErrorOnFailure(aDecoder.Decode(minSetpointDeadBand));
+        if (minSetpointDeadBand < 0)
+        {
+            return CHIP_IM_GLOBAL_STATUS(ConstraintError);
+        }
+        // v1.4: 4.3.9.21 - writes to this attribute SHALL be silently ignored
+        return CHIP_NO_ERROR;
+    }
+    break;
     case RemoteSensing::Id:
         if (localTemperatureNotExposedSupported)
         {