Fix SDL slowness.


git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6373 c046a42c-6fe2-441c-8c8c-71466251a162
diff --git a/sdl.c b/sdl.c
index cddf672..1786992 100644
--- a/sdl.c
+++ b/sdl.c
@@ -62,7 +62,7 @@
     //    printf("updating x=%d y=%d w=%d h=%d\n", x, y, w, h);
 
     SDL_BlitSurface(guest_screen, &rec, real_screen, &rec);
-    SDL_Flip(real_screen);
+    SDL_UpdateRect(real_screen, x, y, w, h);
 }
 
 static void sdl_setdata(DisplayState *ds)