Add missing constness.

llvm-svn: 335711
diff --git a/lldb/source/Target/ThreadPlanStepInRange.cpp b/lldb/source/Target/ThreadPlanStepInRange.cpp
index 5810e9d..6405c13 100644
--- a/lldb/source/Target/ThreadPlanStepInRange.cpp
+++ b/lldb/source/Target/ThreadPlanStepInRange.cpp
@@ -272,7 +272,7 @@
 
         if (bytes_to_skip == 0 && sc.symbol) {
           TargetSP target = m_thread.CalculateTarget();
-          Architecture *arch = target->GetArchitecturePlugin();
+          const Architecture *arch = target->GetArchitecturePlugin();
           if (arch) {
             Address curr_sec_addr;
             target->GetSectionLoadList().ResolveLoadAddress(curr_addr,