Compile fix in qxcbwindow

There was a error: narrowing conversion of 'Myns::XEMBED_VERSION'
from 'unsigned int' to 'long int' inside { } [-Werror=narrowing]

Change-Id: I1e155870b0b632bfe5ffa9deac69c4f151f5aa23
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/plugins/platforms/xcb/qxcbwindow.cpp

@@ -152,7 +152,7 @@ enum QX11EmbedMessageType {
     XEMBED_ACTIVATE_ACCELERATOR = 14
 };
 
-static unsigned int XEMBED_VERSION = 0;
+const long XEMBED_VERSION = 0;
 
 // Returns true if we should set WM_TRANSIENT_FOR on \a w
 static inline bool isTransient(const QWindow *w)