i965: Silence unused parameter warnings

i965: Silence unused parameter warnings

brw_link.cpp:76:44: warning: unused parameter ‘shader_type’ [-Wunused-parameter]
                            gl_shader_stage shader_type,
                                            ^
brw_nir.c: In function ‘brw_nir_lower_vs_inputs’:
brw_nir.c:194:55: warning: unused parameter ‘devinfo’ [-Wunused-parameter]
                         const struct gen_device_info *devinfo,
                                                       ^
brw_vec4_visitor.cpp:914:37: warning: unused parameter ‘sampler’ [-Wunused-parameter]
                            uint32_t sampler,
                                     ^
brw_vec4_visitor.cpp:1146:34: warning: unused parameter ‘stream_id’ [-Wunused-parameter]
 vec4_visitor::gs_emit_vertex(int stream_id)
                                  ^

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Engestrom <eric@engestrom.ch>