samples: rust: pci: take advantage of Devres::access()

For the I/O operations executed from the probe() method, take advantage
of Devres::access(), avoiding the atomic check and RCU read lock required
otherwise entirely.

Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Link: https://lore.kernel.org/r/20250428140137.468709-4-dakr@kernel.org


Signed-off-by: Danilo Krummrich <dakr@kernel.org>