Fix clippy::unnecessary_semicolon warning

```
error: unnecessary semicolon
   --> tools/codegen/src/main.rs:210:18
    |
210 |                 };
    |                  ^ help: remove
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_semicolon
    = note: `-D clippy::unnecessary-semicolon` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::unnecessary_semicolon)]`
```

tools/codegen/src/main.rs

@@ -207,7 +207,7 @@ fn gen_assert_impl() {
                     //         assert_ref_unwind_safe::<crate:: #(#module::)* #ident #lt>();
                     //     });
                     // }
-                };
+                }
             }
             _ => {}
         })