crypto: testmgr - don't copy from source IV too much

While the destination buffer 'iv' is MAX_IVLEN size,
the source 'template[i].iv' could be smaller, thus
memcpy may read read invalid memory.
Use crypto_skcipher_ivsize() to get real ivsize
and pass it to memcpy.

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>