intel/nir: Take nir_shader*s in brw_nir_link_shaders

Since NIR_PASS no longer swaps out the NIR pointer when NIR_TEST_* is
enabled, we can just take a single pointer and not a pointer to pointer.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
10 jobs for !1012 with review/nir-test-fix in 6 minutes and 55 seconds (queued for 1 second)
merge request