Doc: Fix documentation warning in qstylehints.cpp

warning: Command '\snippet (//! [6])' failed at end of file 'code/src_gui_kernel_qguiapplication.cpp'

This change amends 56cd9cc2b0

Change-Id: I63a2f086fc582d3a9c8b60f1ef94ccb537b0d3a5
Reviewed-by: Samuel Gaist <samuel.gaist@edeltech.ch>
Reviewed-by: Sze Howe Koh <szehowe.koh@gmail.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>

src/gui/kernel/qstylehints.cpp

@@ -163,7 +163,7 @@ void QStyleHints::setStartDragDistance(int startDragDistance)
     and the current position (e.g. in the mouse move event) is \c currentPos,
     you can find out if a drag should be started with code like this:
 
-    \snippet code/src_gui_kernel_qguiapplication.cpp 6
+    \snippet code/src_gui_kernel_qapplication.cpp 6
 
     \sa startDragTime(), QPoint::manhattanLength(), {Drag and Drop}
 */