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_function_can_inline.cpp

@@ -59,7 +59,7 @@ bool
 can_inline(ir_call *call)
 {
    ir_function_can_inline_visitor v;
-   const ir_function_signature *callee = call->get_callee();
+   const ir_function_signature *callee = call->callee;
    if (!callee->is_defined)
       return false;