crypto: testmgr - use kmemdup

Fixes coccinnelle alerts:

/crypto/testmgr.c:2112:13-20: WARNING opportunity for kmemdup
/crypto/testmgr.c:2130:13-20: WARNING opportunity for kmemdup
/crypto/testmgr.c:2152:9-16: WARNING opportunity for kmemdup

Signed-off-by: Christopher Diaz Riveros <chrisadr@gentoo.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>