rust: use the `build_error!` macro, not the hidden function

Code and some examples were using the function, rather than the macro. The
macro is what is documented.

Thus move users to the macro.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20241123222849.350287-1-ojeda@kernel.org


[ Applied the change to the new miscdevice cases. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>