crypto: talitos - simplify tests in ipsec_esp()

Do (desc->hdr & DESC_HDR_TYPE_IPSEC_ESP) only once.
Limit number of if/else paths

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>