nouveau: Move fragment exports to the end
Fixes tests on kepler with NV50_PROG_USE_NIR=1, which regressed in b1fa2068:
dEQP-GLES31.functional.shaders.opaque_type_indexing.ubo.uniform_fragment
dEQP-GLES31.functional.shaders.opaque_type_indexing.ubo.dynamically_uniform_fragment
spec@arb_blend_func_extended@arb_blend_func_extended-fbo-extended-blend
spec@arb_blend_func_extended@arb_blend_func_extended-fbo-extended-blend-explicit
spec@arb_blend_func_extended@arb_blend_func_extended-fbo-extended-blend-explicit_gles3
spec@arb_blend_func_extended@arb_blend_func_extended-fbo-extended-blend_gles3
Fixes: b1fa2068