Add some constantness to BranchProbabilityInfo and BlockFrequnencyInfo.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@146986 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/MachineBlockFrequencyInfo.cpp b/lib/CodeGen/MachineBlockFrequencyInfo.cpp
index b92cda9..a079d6e 100644
--- a/lib/CodeGen/MachineBlockFrequencyInfo.cpp
+++ b/lib/CodeGen/MachineBlockFrequencyInfo.cpp
@@ -56,6 +56,6 @@
 /// the other block frequencies. We do this to avoid using of floating points.
 ///
 BlockFrequency MachineBlockFrequencyInfo::
-getBlockFreq(MachineBasicBlock *MBB) const {
+getBlockFreq(const MachineBasicBlock *MBB) const {
   return MBFI->getBlockFreq(MBB);
 }