crypto: af_alg - remove redundant initializations of sk_family

sk_alloc() already sets sock::sk_family to PF_ALG which is passed as the
'family' argument, so there's no need to set it again.

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