cls_bpf: Use kmemdup instead of duplicating it in cls_bpf_prog_from_ops

Replace calls to kmalloc followed by a memcpy with a direct call to
kmemdup.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>