crypto: skcipher - remove redundant check for SKCIPHER_WALK_SLOW

In skcipher_walk_done(), remove the check for SKCIPHER_WALK_SLOW because
it is always true.  All other flags (and lack thereof) were checked
earlier in the function, leaving SKCIPHER_WALK_SLOW as the only
remaining possibility.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>