rust: macros: simplify `format!` arguments

rust: macros: simplify `format!` arguments

Clippy in Rust 1.88.0 (only) reported [1] up to the previous commit:

    warning: variables can be used directly in the `format!` string
       --> rust/macros/module.rs:112:23
        |
    112 |         let content = format!("{param}:{content}", param = param, content = content);
        |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#uninlined_format_args
        = note: `-W clippy::uninlined-format-args` implied by `-W clippy::all`
        = help: to override `-W clippy::all` add `#[allow(clippy::uninlined_format_args)]`
    help: change this to
        |
    112 -         let content = format!("{param}:{content}", param = param, content = content);
    112 +         let content = format!("{param}:{content}");

The reason it only triggers in that version is that the lint was moved
from `pedantic` to `style` in Rust 1.88.0 and then back to `pedantic`
in Rust 1.89.0 [2][3].

In this case, the suggestion is fair and a pure simplification, thus
just apply it.

In addition, do the same for another place in the file that Clippy does
not report because it is multi-line.

Link: https://lore.kernel.org/rust-for-linux/CANiq72=drAtf3y_DZ-2o4jb6Az9J3Yj4QYwWnbRui4sm4AJD3Q@mail.gmail.com/
Link: https://github.com/rust-lang/rust-clippy/pull/15287
Link: https://github.com/rust-lang/rust-clippy/issues/15151
Reviewed-by: Gary Guo <gary@garyguo.net>
Acked-by: Sami Tolvanen <samitolvanen@google.com>
Link: https://patch.msgid.link/20260331205849.498295-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>