Use kmemdup rather than duplicating its implementation

Generated by: scripts/coccinelle/api/memdup.cocci

Fixes: f08fcced ("crypto: allwinner - Add sun8i-ss cryptographic offloader")
CC: Corentin Labbe <clabbe.montjoie@gmail.com>
Signed-off-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>