Address review comments.

src/darwin/Framework/CHIP/MTRDeviceController.mm

@@ -112,6 +112,10 @@
 
 using namespace chip::Tracing::DarwinFramework;
 
+@interface MTRDeviceController ()
+@property (readwrite, nonatomic) NSUUID * uniqueIdentifier;
+@end
+
 @implementation MTRDeviceController {
     chip::Controller::DeviceCommissioner * _cppCommissioner;
     chip::Credentials::PartialDACVerifier * _partialDACVerifier;
@@ -154,7 +158,7 @@ - (instancetype)initForSubclasses:(BOOL)startSuspended uniqueIdentifier:(NSUUID
         // nothing, as superclass of MTRDeviceController is NSObject
     }
 
-    _uniqueIdentifier = uniqueIdentifier;
+    self.uniqueIdentifier = uniqueIdentifier;
 
     _underlyingDeviceMapLock = OS_UNFAIR_LOCK_INIT;
 
@@ -165,7 +169,8 @@ - (instancetype)initForSubclasses:(BOOL)startSuspended uniqueIdentifier:(NSUUID
 
     // All synchronous suspend/resume activity has to be protected by
     // @synchronized(self), so that parts of suspend/resume can't
-    // interleave with each other.
+    // interleave with each other. Using @synchronized here because
+    // MTRDevice may call isSuspended.
     _suspended = startSuspended;
 
     _nodeIDToDeviceMap = [NSMapTable strongToWeakObjectsMapTable];
@@ -354,7 +359,6 @@ - (BOOL)isRunning
 
 - (BOOL)isSuspended
 {
-    // Using @synchronized here because MTRDevice may call isSuspended.
     @synchronized(self) {
         return _suspended;
     }