rust: alloc: align Debug implementation for Box with Display

Ensure consistency between `Debug` and `Display` for `Box` by
updating `Debug` to match the new `Display` style.

Acked-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Guangbo Cui <2407018371@qq.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/tencent_1FC0BC283DA65DD81A8A14EEF25563934E05@qq.com
[ Reworded title. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: JCKeep

rust/kernel/alloc/kbox.rs

@@ -443,7 +443,7 @@ where
     A: Allocator,
 {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fmt::Debug::fmt(&**self, f)
+        <T as fmt::Debug>::fmt(&**self, f)
     }
 }