Fix note message from gcc about uninitialized member

After change to c++17, on Tizen, we've got a note message from gcc about
uninitialized member of ChipError class in a lambda function. This is a
false positive report, but by initializing CHIP_ERROR variable we can
get rid of it and get a clean build once again.

src/app/clusters/access-control-server/access-control-server.cpp

@@ -177,7 +177,7 @@ CHIP_ERROR AccessControlAttribute::ReadAcl(AttributeValueEncoder & aEncoder)
         {
             auto fabric = info.GetFabricIndex();
             ReturnErrorOnFailure(GetAccessControl().Entries(fabric, iterator));
-            CHIP_ERROR err;
+            CHIP_ERROR err = CHIP_NO_ERROR;
             while ((err = iterator.Next(entry)) == CHIP_NO_ERROR)
             {
                 ReturnErrorOnFailure(encoder.Encode(encodableEntry));