dri2: Only invalidate the immediate Window upon SetWindowPixmap

All callers of SetWindowPixmap will themselves be traversing the Window
heirarchy updating the backing Pixmap of each child and so we can forgo
doing the identical traversal inside the DRI2SetWindowPixmap handler.
Reported-by: Loïc Yhuel <loic.yhuel@gmail.com>
Link: http://lists.x.org/archives/xorg-devel/2015-February/045638.htmlSigned-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

hw/xfree86/dri2/dri2.c

@@ -1385,8 +1385,7 @@ DRI2ConfigNotify(WindowPtr pWin, int x, int y, int w, int h, int bw,
 static void
 DRI2SetWindowPixmap(WindowPtr pWin, PixmapPtr pPix)
 {
-    DrawablePtr pDraw = (DrawablePtr) pWin;
-    ScreenPtr pScreen = pDraw->pScreen;
+    ScreenPtr pScreen = pWin->drawable.pScreen;
     DRI2ScreenPtr ds = DRI2GetScreen(pScreen);
 
     pScreen->SetWindowPixmap = ds->SetWindowPixmap;
@@ -1394,7 +1393,7 @@ DRI2SetWindowPixmap(WindowPtr pWin, PixmapPtr pPix)
     ds->SetWindowPixmap = pScreen->SetWindowPixmap;
     pScreen->SetWindowPixmap = DRI2SetWindowPixmap;
 
-    DRI2InvalidateDrawableAll(pDraw);
+    DRI2InvalidateDrawable(&pWin->drawable);
 }
 
 #define MAX_PRIME DRI2DriverPrimeMask