Use kmemdup rather than duplicating its implementation.

Generated by: scripts/coccinelle/api/memdup.cocci
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>