crypto: testmgr - make test_skcipher also test 'dst != src' code paths

Currrently test_skcipher uses same buffer for destination and source. However
in any places, 'dst != src' take different path than 'dst == src' case.

Therefore make test_skcipher also run tests with destination buffer being
different than source buffer.

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>