Use the rel_pc instead of computing it.

Bug: 23762183

Test: Compiles.
Change-Id: I5fe96c444bed89b4b9d3e96ffc37555678428be1
diff --git a/runtime/native_stack_dump.cc b/runtime/native_stack_dump.cc
index cbff0bb..7e16357 100644
--- a/runtime/native_stack_dump.cc
+++ b/runtime/native_stack_dump.cc
@@ -337,7 +337,7 @@
     } else {
       os << StringPrintf(Is64BitInstructionSet(kRuntimeISA) ? "%016" PRIxPTR "  "
                                                             : "%08" PRIxPTR "  ",
-                         BacktraceMap::GetRelativePc(it->map, it->pc));
+                         it->rel_pc);
       os << it->map.name;
       os << " (";
       if (!it->func_name.empty()) {