[OpenCL] Enables passing sampler initializer to function argument

Reviewers: Anastasia, cfe-commits

Reviewed By: Anastasia

Subscribers: yaxunl, bader

Differential Revision: https://reviews.llvm.org/D31594

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@299524 91177308-0d34-0410-b5e6-96231b3b80d8