crypto: algif_skcipher - Fix race condition in skcipher_check_key

    commit 1822793a523e5d5730b19cc21160ff1717421bc8 upstream.

    We need to lock the child socket in skcipher_check_key as otherwise
    two simultaneous calls can cause the parent socket to be freed.

    Cc: stable@vger.kernel.org
    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>