rust: devres: do not dereference to the internal Revocable

rust: devres: do not dereference to the internal Revocable

We can't expose direct access to the internal Revocable, since this
allows users to directly revoke the internal Revocable without Devres
having the chance to synchronize with the devres callback -- we have to
guarantee that the internal Revocable has been fully revoked before
the device is fully unbound.

Hence, remove the corresponding Deref implementation and, instead,
provide indirect accessors for the internal Revocable.

Note that we can still support Devres::revoke() by implementing the
required synchronization (which would be almost identical to the
synchronization in Devres::drop()).

Fixes: 76c01ded724b ("rust: add devres abstraction")
Reviewed-by: Benno Lossin <lossin@kernel.org>
Link: https://lore.kernel.org/r/20250611174827.380555-1-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>