vp10_alloc_context_buffers: clear cm->mi* on failure

based on:
8b4c315 vp9_alloc_context_buffers: clear cm->mi* on failure

Change-Id: I3438a052721b960ff178cb647780f11bc33571fe
diff --git a/vp10/common/alloccommon.c b/vp10/common/alloccommon.c
index be2e538..10b4bf1 100644
--- a/vp10/common/alloccommon.c
+++ b/vp10/common/alloccommon.c
@@ -151,6 +151,8 @@
   return 0;
 
 fail:
+  // clear the mi_* values to force a realloc on resync
+  vp10_set_mb_mi(cm, 0, 0);
   vp10_free_context_buffers(cm);
   return 1;
 }