i965/vec4: Silence a couple unused parameter warnings

brw_vec4_visitor.cpp:2717:1: warning: unused parameter 'ir' [-Wunused-parameter]
brw_vec4_visitor.cpp:2723:1: warning: unused parameter 'ir' [-Wunused-parameter]

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>

src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp

@@ -2655,13 +2655,13 @@ vec4_visitor::swizzle_result(ir_texture *ir, src_reg orig_val, int sampler)
 }
 
 void
-vec4_visitor::visit(ir_return *ir)
+vec4_visitor::visit(ir_return *)
 {
    assert(!"not reached");
 }
 
 void
-vec4_visitor::visit(ir_discard *ir)
+vec4_visitor::visit(ir_discard *)
 {
    assert(!"not reached");
 }