carl9170: devres-ing hwrng_register usage

devres will take care of freeing the hwrng once it is no longer needed.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/d1c16490462a9371ab3cc16a018ef5e08382a35e.1646250537.git.chunkeey@gmail.com