rust_binder: use `kernel::fmt`

Reduce coupling to implementation details of the formatting machinery by
avoiding direct use for `core`'s formatting traits and macros.

This backslid in commit eafedbc7c050 ("rust_binder: add Rust Binder
driver").

Reviewed-by: Alice Ryhl <[e-mail]>
Signed-off-by: Tamir Duberstein <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Miguel Ojeda <[e-mail]>

drivers/android/binder/error.rs

···
 
 // Copyright (C) 2025 Google LLC.
 
+use kernel::fmt;
 use kernel::prelude::*;
 
 use crate::defs::*;
···
     }
 }
 
-impl core::fmt::Debug for BinderError {
-    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+impl fmt::Debug for BinderError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self.reply {
             BR_FAILED_REPLY => match self.source.as_ref() {
                 Some(source) => f