[OPENCL] Fix wrongly vla error for OpenCL array.

Summary:
OpenCL should support array with const value size length, those const
varibale in global and constant address space and variable in constant
address space.

Fixed test case error.

Reviewers: Anastasia, yaxunl, bader

Subscribers: bader, cfe-commits

Differential Revision: http://reviews.llvm.org/D20090

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@271978 91177308-0d34-0410-b5e6-96231b3b80d8