vp8: Switch skin model to mode 0 to save some cycle.

This change will speed up vp8 encoder by 1.5% ~ 2% on linux. No
much speed change on Mac.

Change-Id: Id957f19ddd89805baa2af84c5027d52d9a48553f
diff --git a/vp8/encoder/pickinter.c b/vp8/encoder/pickinter.c
index 7948657..b6e8dbf 100644
--- a/vp8/encoder/pickinter.c
+++ b/vp8/encoder/pickinter.c
@@ -35,7 +35,7 @@
 extern unsigned int cnt_pm;
 #endif
 
-#define MODEL_MODE 1
+#define MODEL_MODE 0
 
 extern const int vp8_ref_frame_order[MAX_MODES];
 extern const MB_PREDICTION_MODE vp8_mode_order[MAX_MODES];