PATCH: fix clang to emit correct addrspacecast for CUDA

[Matt Arsenault]

On 03/24/2014 11:46 AM, Justin Holewinski wrote:
>  Of course, this also assumes address space 0 is generic.  This is 
> currently true for the in-tree targets and CUDA/OpenCL support in 
> Clang, but I don't believe its a set rule anywhere.

R600 wants this optimization, except the "generic" address space isn't 
0, and is instead some other currently undefined number.

-Matt