Make a method const, no functionality changes

llvm-svn: 15193
diff --git a/llvm/lib/CodeGen/LiveInterval.h b/llvm/lib/CodeGen/LiveInterval.h
index 673dc7f..d23e413 100644
--- a/llvm/lib/CodeGen/LiveInterval.h
+++ b/llvm/lib/CodeGen/LiveInterval.h
@@ -112,7 +112,7 @@
 
     /// getLiveRangeContaining - Return the live range that contains the
     /// specified index, or null if there is none.
-    LiveRange *getLiveRangeContaining(unsigned Idx);
+    const LiveRange *getLiveRangeContaining(unsigned Idx) const;
 
 
     /// joinable - Two intervals are joinable if the either don't overlap at all