crypto: twofish-avx - remove useless instruction

The register %rdx is written, but never read till the end of the encryption
routine. Therefore let's delete the useless instruction.

Signed-off-by: Johannes Goetzfried <Johannes.Goetzfried@informatik.stud.uni-erlangen.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>