iOS: Put common IosDevice constructor code into a function

It is not even clear that the remaining difference are needed.

Change-Id: Ic4418143242793d82a1f4c4c368af69a2e537078
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/ios/iosdevice.h

@@ -68,6 +68,9 @@ protected:
     IosDevice();
     IosDevice(const QString &uid);
 
+    enum CtorHelper {};
+    IosDevice(CtorHelper);
+
     Dict m_extraInfo;
     bool m_ignoreDevice = false;
     mutable quint16 m_lastPort;