crypto: scatterwalk - Remove unnecessary aliasing check in map_and_copy

The aliasing check in map_and_copy is no longer necessary because
the IPsec ESP code no longer provides an IV that points into the
actual request data.  As this check is now triggering BUG checks
due to the vmalloced stack code, I'm removing it.

Reported-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>