rust/faux: Drop #[repr(transparent)] from faux::Registration

rust/faux: Drop #[repr(transparent)] from faux::Registration

I think this change got missed during review, we don't need
 #[repr(transparent)] since Registration just holds a single NonNull. This
attribute had originally been added by me when I was still figuring out how
the bindings should look like but got committed by mistake. So, just drop
it.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Reviewed-by: Fiona Behrens <me@Kloenk.dev>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20250225213112.872264-2-lyude@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>