rust: sync: use kernel::{fmt,prelude::fmt!}

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

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

rust/kernel/sync/arc.rs

@@ -20,6 +20,7 @@
     alloc::{AllocError, Flags, KBox},
     bindings,
     ffi::c_void,
+    fmt,
     init::InPlaceInit,
     try_init,
     types::{ForeignOwnable, Opaque},
@@ -27,7 +28,6 @@
 use core::{
     alloc::Layout,
     borrow::{Borrow, BorrowMut},
-    fmt,
     marker::PhantomData,
     mem::{ManuallyDrop, MaybeUninit},
     ops::{Deref, DerefMut},