[CRYPTO] api: fix writting into unallocated memory in setkey_aligned

setkey_unaligned() commited in ca7c3938
overwrites unallocated memory in the following memset() because
I used the wrong buffer length.

Signed-off-by: Sebastian Siewior <sebastian@breakpoint.cc>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>