vpx_dsp/bitreader.h: vp9_->vpx_

Replace vp9_ in names to vpx_ as they are not codec specific.

Change-Id: I2e583aa63dee769353ada4b42417aa15c4074ebb
diff --git a/vpx_dsp/prob.c b/vpx_dsp/prob.c
index 8f44e18..b88f0e4 100644
--- a/vpx_dsp/prob.c
+++ b/vpx_dsp/prob.c
@@ -31,9 +31,9 @@
 
 static unsigned int tree_merge_probs_impl(unsigned int i,
                                           const vp9_tree_index *tree,
-                                          const vp9_prob *pre_probs,
+                                          const vpx_prob *pre_probs,
                                           const unsigned int *counts,
-                                          vp9_prob *probs) {
+                                          vpx_prob *probs) {
   const int l = tree[i];
   const unsigned int left_count = (l <= 0)
                  ? counts[-l]
@@ -47,7 +47,7 @@
   return left_count + right_count;
 }
 
-void vp9_tree_merge_probs(const vp9_tree_index *tree, const vp9_prob *pre_probs,
-                          const unsigned int *counts, vp9_prob *probs) {
+void vp9_tree_merge_probs(const vp9_tree_index *tree, const vpx_prob *pre_probs,
+                          const unsigned int *counts, vpx_prob *probs) {
   tree_merge_probs_impl(0, tree, pre_probs, counts, probs);
 }