A platform device's remove callback is only ever called after the probe
callback returned success.

In the case of kmb_ocs_aes_remove() this means that kmb_ocs_aes_probe()
succeeded before and so platform_set_drvdata() was called with a
non-zero argument and platform_get_drvdata() returns non-NULL.

This prepares making remove callbacks return void.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>