CodeGen: Fix invalid bitcast for coerced function argument

Clang assumes coerced function argument is in address space 0, which is not always true and results in invalid bitcasts.

This patch fixes failure in OpenCL conformance test api/get_kernel_arg_info with amdgcn---amdgizcl triple, where non-zero alloca address space is used.

Differential Revision: https://reviews.llvm.org/D34777

llvm-svn: 306721