crypto: xts - Fix an error handling path in 'create()'

All error handling paths 'goto err_drop_spawn' except this one.
In order to avoid some resources leak, we should do it as well here.

Fixes: f1c131b4

 ("crypto: xts - Convert to skcipher")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>