mesa: keep track of the current variable in add_uniform_to_shader

Bindless samplers are considered PROGRAM_UNIFORM but
add_uniform_to_shader::visit_field() is based on glsl_type.

Because only ir_variable knows if the uniform variable is
bindless via ir_variable::bindless, store it instead of
adding a new parameter to visit_field().

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>

src/mesa/program/ir_to_mesa.cpp

@@ -2420,6 +2420,7 @@ public:
    void process(ir_variable *var)
    {
       this->idx = -1;
+      this->var = var;
       this->program_resource_visitor::process(var);
       var->data.param_index = this->idx;
    }
@@ -2433,6 +2434,7 @@ private:
    struct gl_shader_program *shader_program;
    struct gl_program_parameter_list *params;
    int idx;
+   ir_variable *var;
    gl_shader_stage shader_type;
 };