crypto: s390/aes - drop redundant xts key check

xts_fallback_setkey() in xts_aes_set_key() will now enforce key size
rule in FIPS mode when setting up the fallback algorithm keys, which
makes the check in xts_aes_set_key() redundant or unreachable. So just
drop this check.

xts_fallback_setkey() now makes a key size check in xts_verify_key():

xts_fallback_setkey()
  crypto_skcipher_setkey() [ skcipher_setkey_unaligned() ]
    cipher->setkey() { .setkey = xts_setkey }
      xts_setkey()
        xts_verify_key()

Signed-off-by: Vladis Dronov <vdronov@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>