Reduce blk_skip array size

Reduce the blk_skip array size to the maximum txb numbers in a
coding block. This makes the speed 1 about 5% faster for smaller
resolution clips.

Change-Id: I1812dc4d403e08f0566ead8a14c6046e505bb849
diff --git a/av1/encoder/block.h b/av1/encoder/block.h
index 646edb5..d438c98 100644
--- a/av1/encoder/block.h
+++ b/av1/encoder/block.h
@@ -247,8 +247,8 @@
   // from extending outside the UMV borders
   MvLimits mv_limits;
 
-  uint8_t blk_skip[MAX_MB_PLANE][MAX_MIB_SIZE * MAX_MIB_SIZE * 8];
-  uint8_t blk_skip_drl[MAX_MB_PLANE][MAX_MIB_SIZE * MAX_MIB_SIZE * 8];
+  uint8_t blk_skip[MAX_MB_PLANE][MAX_MIB_SIZE * MAX_MIB_SIZE];
+  uint8_t blk_skip_drl[MAX_MB_PLANE][MAX_MIB_SIZE * MAX_MIB_SIZE];
 
   int skip;
   int skip_chroma_rd;