Address review comments.

Co-authored-by: Karsten Sperling <113487422+ksperling-apple@users.noreply.github.com>

src/darwin/Framework/CHIP/MTRBaseDevice.h

@@ -238,8 +238,9 @@ typedef NS_ENUM(uint8_t, MTRTransportType) {
  *                    passed to the completion, so values will only be passed in
  *                    when the write succeeds.  In that case, values will have
  *                    the format documented in the definition of
- *                    MTRDeviceResponseHandler and just contain a single entry
- *                    with the path of the attribute that was written.
+ *                    MTRDeviceResponseHandler and will be an array with a single element
+ *                    which is a dictionary that has a MTRAttributePathKey entry in it, whose value
+ *                    is the attribute path that was successfully written to.
  */
 - (void)writeAttributeWithEndpointID:(NSNumber *)endpointID
                            clusterID:(NSNumber *)clusterID

src/darwin/Framework/CHIP/MTRBaseDevice.mm

@@ -955,8 +955,7 @@ - (void)writeAttributeWithEndpointID:(NSNumber *)endpointID
             // Controller::WriteAttribute guarantees that there will be exactly one call to either the success callback or the
             // failure callback, for a non-group session.
             auto onSuccessCb = [successCb, bridge](const app::ConcreteAttributePath & attribPath) {
-                auto resultArray = [[NSMutableArray alloc] init];
-                [resultArray addObject:@ { MTRAttributePathKey : [[MTRAttributePath alloc] initWithPath:attribPath] }];
+                auto resultArray = @[ @{ MTRAttributePathKey : [[MTRAttributePath alloc] initWithPath:attribPath] }] ];
                 successCb(bridge, resultArray);
             };