glsl: Remove ir_call::get_callee() and set_callee().

Previously, set_callee() performed some assertions about the type of the
ir_call; protecting the bare pointer ensured these checks would be run.

However, ir_call no longer has a type, so the getter and setter methods
don't actually do anything useful.  Remove them in favor of accessing
callee directly, as is done with most other fields in our IR.

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

src/glsl/ir_validate.cpp

@@ -541,7 +541,7 @@ ir_validate::visit_enter(ir_assignment *ir)
 ir_visitor_status
 ir_validate::visit_enter(ir_call *ir)
 {
-   ir_function_signature *const callee = ir->get_callee();
+   ir_function_signature *const callee = ir->callee;
 
    if (callee->ir_type != ir_type_function_signature) {
       printf("IR called by ir_call is not ir_function_signature!\n");