crypto: atmel-aes - Drop if with an always false condition

The remove callback is only called after probe completed successfully.
In this case platform_set_drvdata() was called with a non-NULL argument
and so aes_dd is never NULL.

This is a preparation for making platform 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>