Add the code that sets previous value in the block where we have an e…

…xpected value

src/darwin/Framework/CHIP/MTRDevice.mm

@@ -2144,6 +2144,7 @@ - (NSArray *)_getAttributesToReportWithReportedValues:(NSArray<NSDictionary<NSSt
             // if expected values exists, purge and update read cache
             NSArray * expectedValue = _expectedValueCache[attributePath];
             if (expectedValue) {
+                previousValue = expectedValue[MTRDeviceExpectedValueFieldValueIndex];
                 _readCache[attributePath] = attributeDataValue;
                 shouldReportAttribute = NO;
             } else if (readCacheValueChanged) {