Fix clippy::precedence warning

[psychon]

With Rust 1.85.0, clippy started warning:

error: operator precedence can trip the unwary
   --> xcbgen-rs/src/defs/alignment.rs:258:30
    |
258 |                 incr = 1 << (incr | base | 1 << 31).trailing_zeros().min(31);
    |                              ^^^^^^^^^^^^^^^^^^^^^ help: consider parenthesizing your expression: `incr | base | (1 << 31)`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence
    = note: `-D clippy::precedence` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::precedence)]`

This commit simply follows clippy's suggestion.