rust: miscdevice: fix warning on c_uint to u32 cast

When building miscdevice with clippy warnings, the following warning is
emitted:

	warning: casting to the same type is unnecessary (`u32` -> `u32`)
	   --> /home/aliceryhl/rust-for-linux/rust/kernel/miscdevice.rs:220:28
	    |
	220 |     match T::ioctl(device, cmd as u32, arg as usize) {
	    |                            ^^^^^^^^^^ help: try: `cmd`
	    |
	    = help: for further information visit
	      https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast


	    = note: `-W clippy::unnecessary-cast` implied by `-W clippy::all`
	    = help: to override `-W clippy::all` add `#[allow(clippy::unnecessary_cast)]`

Thus, fix it.

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20241015-miscdevice-cint-cast-v1-1-fcf4b75700ac@google.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>