Fix deref expecting a codegenptr and not borrow

examples/ptr_hard.reid

@@ -1,6 +1,7 @@
-fn main() {
+fn main() -> u8 {
     let mut a = 5;
     inner(&mut a);
+    return 0;
 }
 
 fn inner(a: &mut i32) {

reid/src/codegen.rs

@@ -1179,7 +1179,7 @@ impl mir::Expression {
 
                 Some({
                     if state.should_load {
-                        if let TypeKind::CodegenPtr(inner) = *ptr_inner.clone() {
+                        if let TypeKind::Borrow(inner, _) = *ptr_inner.clone() {
                             StackValue(
                                 v.0.derive(
                                     scope