rust: cpufreq: suppress clippy::double_parens in Policy doctest

rust: cpufreq: suppress clippy::double_parens in Policy doctest

The kernel fmt! proc macro wraps each format argument as &(arg). Passing a
tuple such as (a, b) produces &((a, b)) after expansion. Clippy flags that
as double_parens, but it is a false positive fixed in Clippy 1.92 [1] [2].

Suppress the warning on the affected doctest function with a reason
attribute so it can be removed once the minimum toolchain moves past 1.92.

[ We may end up deciding to support per-version Clippy lints, in which
  case we will need [3].

  In the future, if [4] gets fixed, we may be able to use
  `Delimiter::None` as Gary suggested in [5].

Link: https://lore.kernel.org/rust-for-linux/20260307170929.153892-1-ojeda@kernel.org/
Link: https://github.com/rust-lang/rust/issues/67062
Link: https://lore.kernel.org/rust-for-linux/DGUA5GY2DGYN.3PG0FKLG7GFN1@garyguo.net/
    - Miguel ]

Link: https://github.com/rust-lang/rust-clippy/issues/15852
Link: https://github.com/rust-lang/rust-clippy/pull/15939
Suggested-by: Gary Guo <gary@garyguo.net>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://patch.msgid.link/20260312041934.362840-2-jhubbard@nvidia.com
[ Reworded to replace GitHub-like short link with full URLs in Link tags.
  Reworded reason string to match the style of a couple others we have
  elsewhere. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>