crypto: essiv - Check ssize for decryption and in-place encryption

Move the ssize check to the start in essiv_aead_crypt so that
it's also checked for decryption and in-place encryption.

Reported-by: Muhammad Alifa Ramdhan <ramdhan@starlabs.sg>
Fixes: be1eb7f7 ("crypto: essiv - create wrapper template for ESSIV generation")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>