(!1710) xwin: fix memleak on freeing pixmaps

Xwin's DestroyPixmap proc just free()s the PixmapRec directly, w/o catering
for devPrivate's, so leaving a memleak. The correct DIX function for this
is FreePixmap().

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>

hw/xwin/winmultiwindowwindow.c

@@ -1137,9 +1137,7 @@ winDestroyPixmapMultiwindow(PixmapPtr pPixmap)
     pPixmapPriv->pbmih = NULL;
 
     /* Free the pixmap memory */
-    free(pPixmap);
-    pPixmap = NULL;
-
+    FreePixmap(pPixmap);
     return TRUE;
 }