QColorDialog: code tidies

Combine two flag-like enumerations using a bitwise OR, not a plus.
Cleanup for the follow-up commits.

Change-Id: Iceb05bf5ea0635d623ba9a7d145606e80b7f21f3
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/widgets/dialogs/qcolordialog.cpp

@@ -1784,7 +1784,7 @@ void QColorDialogPrivate::initWidgets()
     pickLay->addLayout(cLay);
     cp = new QColorPicker(q);
 
-    cp->setFrameStyle(QFrame::Panel + QFrame::Sunken);
+    cp->setFrameStyle(QFrame::Panel | QFrame::Sunken);
 
 #if defined(QT_SMALL_COLORDIALOG)
     cp->hide();