Changed a constant array to static const type

Change-Id: I5b3918441f63ceb7889dcf546e9a2d781be4a3cb

vp9/encoder/vp9_pickmode.c

diff --git a/vp9/encoder/vp9_pickmode.c b/vp9/encoder/vp9_pickmode.c
index a4e11d6..383d927 100644
--- a/vp9/encoder/vp9_pickmode.c
+++ b/vp9/encoder/vp9_pickmode.c
@@ -192,7 +192,7 @@
                                     VP9_ALT_FLAG };
   int64_t best_rd = INT64_MAX;
   int64_t this_rd;
-  int64_t cost[4]= { 0, 50, 75, 100 };
+  static const int cost[4]= { 0, 50, 75, 100 };
 
   const int64_t inter_mode_thresh = 300;
   const int64_t intra_mode_cost = 50;