Fixed a size hint issue with combo box

Change-Id: I6cd39d5f3d3c0a767759abbb043277cd5ae83d2a
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>

src/styles/Desktop/ComboBoxStyle.qml

@@ -57,6 +57,7 @@ Item {
         text: comboBox.selectedText
         hasFocus: comboBox.focus
         contentHeight: 18
+        contentWidth: 80
         Component.onCompleted: popup.center = styleHint("comboboxpopup");
     }
 }