Fix the "DFA out of memory" error for the reverse Prog.

Change-Id: If9a1914e7b598b21dabd81ef61293368c15587f6
Reviewed-on: https://code-review.googlesource.com/30230
Reviewed-by: Paul Wankadia <junyer@google.com>

re2/re2.cc

diff --git a/re2/re2.cc b/re2/re2.cc
index 7d787a8..3f28ba3 100644
--- a/re2/re2.cc
+++ b/re2/re2.cc
@@ -668,9 +668,9 @@
                            Prog::kLongestMatch, &match, &dfa_failed, NULL)) {
         if (dfa_failed) {
           if (options_.log_errors())
-            LOG(ERROR) << "DFA out of memory: size " << prog_->size() << ", "
-                       << "bytemap range " << prog_->bytemap_range() << ", "
-                       << "list count " << prog_->list_count();
+            LOG(ERROR) << "DFA out of memory: size " << prog->size() << ", "
+                       << "bytemap range " << prog->bytemap_range() << ", "
+                       << "list count " << prog->list_count();
           // Fall back to NFA below.
           skipped_test = true;
           break;