crypto: sahara - remove unused error field in sahara_dev

The "error" field in sahara_dev struct hasn't been needed/used since commit
c0c3c89a

 ("crypto: sahara - replace tasklets with kthread"), so remove
the remaining references.

Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>