intel/compiler: Always apply sample mask on Vulkan.

intel/compiler: Always apply sample mask on Vulkan.

With OpenGL, shader writes to the sample mask are ignored when not
rendering to a multisample render target. However, on Vulkan, writes to
the sample mask have still have their effect in that case.

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/3016
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5156>