rust: cpufreq: replace `MaybeUninit::zeroed().assume_init()` with `pin_init::zeroed()`

rust: cpufreq: replace `MaybeUninit::zeroed().assume_init()` with `pin_init::zeroed()`

All types in `bindings` implement `Zeroable` if they can, so use
`pin_init::zeroed` instead of relying on `unsafe` code.

If this ends up not compiling in the future, something in bindgen or on
the C side changed and is most likely incorrect.

Signed-off-by: Benno Lossin <lossin@kernel.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>