rust: miscdevice: use `pin_init::zeroed()` for C type initialization

rust: miscdevice: use `pin_init::zeroed()` for C type initialization

Replace manual zero-initialization using
`MaybeUninit::zeroed().assume_init()` with `pin_init::zeroed()`.
The `pin_init` helper provides a safer and clearer API for
zero-initializing C structs without requiring an `unsafe` block.

Link: https://github.com/Rust-for-Linux/linux/issues/1189
Signed-off-by: Atharv Dubey <atharvd440@gmail.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://patch.msgid.link/20251129121513.20738-1-atharvd440@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>