[tracking] Fix deduced type

'auto' doesn't pick up the reference-type returned from tracking(),
and 'auto&' reads funny to me, so make the type explicit.

src/modules/tracking/TrackingViewStep.cpp

@@ -151,7 +151,7 @@ QVariantMap TrackingViewStep::setTrackingOption(const QVariantMap& configuration
     }
     cDebug() << "  .. settable=" << settingEnabled << "default=" << userEnabled;
 
-    auto trackingConfiguration = tracking( t );
+    TrackingEnabled& trackingConfiguration = tracking( t );
     trackingConfiguration.settingEnabled = settingEnabled;
     trackingConfiguration.userEnabled = userEnabled;