rust: error: replace match + panic in const context with const expect

This patch replaces an instance of match + panic with const expect,
which is now usable in const contexts after the MSRV was updated to
1.85.0 (it was available since Rust 1.83.0).

Suggested-by: Gary Guo <gary@garyguo.net>
Link: #1229
Signed-off-by: Daniel del Castillo <delcastillodelarosadaniel@gmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20260408200949.99059-1-delcastillodelarosadaniel@gmail.com
[ Adjusted Git author's name with the Signed-off-by value. Reworded
  slightly and removed duplicated word. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: CastilloDel

rust/kernel/error.rs

@@ -25,10 +25,8 @@ pub mod code {
             #[doc = $doc]
             )*
             pub const $err: super::Error =
-                match super::Error::try_from_errno(-(crate::bindings::$err as i32)) {
-                    Some(err) => err,
-                    None => panic!("Invalid errno in `declare_err!`"),
-                };
+                super::Error::try_from_errno(-(crate::bindings::$err as i32))
+                    .expect("Invalid errno in `declare_err!`");
         };
     }