pwm: Fix Rust formatting

pwm: Fix Rust formatting

We do our best to keep the repository `rustfmt`-clean [1], thus run the
tool to fix the formatting issue.

A trailing empty comment [2] is added in order to preserve the wanted
style for imports (otherwise the tool will compact the first two items).

Link: https://rust-for-linux.com/contributing#submit-checklist-addendum
Link: https://docs.kernel.org/rust/coding-guidelines.html#style-formatting
Fixes: d8046cd50879 ("rust: pwm: Add complete abstraction layer")
Fixes: 7b3dce814a15 ("rust: pwm: Add Kconfig and basic data structures")
Fixes: e03724aac758 ("pwm: Add Rust driver for T-HEAD TH1520 SoC")
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Link: https://patch.msgid.link/20251029182502.783392-1-ojeda@kernel.org
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>