intel/compiler: Use nir's info when checking uses_streams.

intel/compiler: Use nir's info when checking uses_streams.

Vulkan and Gallium don't use Mesa's gl_program data structure, so they
can't poke at 'prog'.  But we can simply use the copy of the shader info
stored with the NIR shader, which is guaranteed to exist.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>