rust: cpufreq: Ensure C ABI compatibility in all unsafe

Update all `unsafe extern "C"` callback functions in the cpufreq module to
use `kernel::ffi` types (`c_int`, `c_uint`, etc.) instead of Rust-native
types like `i32`, `u32`, or `usize`.

This change ensures that all Rust callbacks have signatures that are
ABI-compatible with their corresponding C counterparts, which is critical
for FFI correctness and safety.

Suggested-by: Miguel Ojeda <ojeda@kernel.org>
Link: https://github.com/Rust-for-Linux/linux/issues/1170


Signed-off-by: Abhinav Ananthu <abhinav.ogl@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>