crypto: testmgr - fix sglen in test_aead for case 'dst != src'

Commit d8a32ac2

 (crypto: testmgr - make
test_aead also test 'dst != src' code paths) added support for different
source and destination buffers in test_aead.

This patch modifies the source and destination buffer lengths accordingly:
the lengths are not equal since encryption / decryption adds / removes
the ICV.

Cc: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Signed-off-by: Horia Geanta <horia.geanta@freescale.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>