crypto: omap-aes - remove the sysfs group during driver removal

The driver removal should also cleanup the created sysfs group. If not,
the driver fails the subsequent probe as the files exist already. Also,
drop a completely unnecessary pointer assignment from the removal
function at the same time.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>