Fix problems in "[OpenCL] Enabling the usage of CLK_NULL_QUEUE as compare operand."

Summary: Fixed warnings in commit: https://reviews.llvm.org/rL290171

Reviewers: djasper, Anastasia

Subscribers: yaxunl, cfe-commits, bader

Differential Revision: https://reviews.llvm.org/D27981

llvm-svn: 290431
diff --git a/clang/lib/CodeGen/CGExprConstant.cpp b/clang/lib/CodeGen/CGExprConstant.cpp
index 752f419..62a9c8f 100644
--- a/clang/lib/CodeGen/CGExprConstant.cpp
+++ b/clang/lib/CodeGen/CGExprConstant.cpp
@@ -753,6 +753,7 @@
     case CK_FloatingToBoolean:
     case CK_FloatingCast:
     case CK_ZeroToOCLEvent:
+    case CK_ZeroToOCLQueue:
       return nullptr;
     }
     llvm_unreachable("Invalid CastKind");