bpf: verifier: Use copy_array for jmp_history

Eliminate a couple needless kfree / kmalloc cycles by using
copy_array for jmp_history.

Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210429134656.122225-3-lmb@cloudflare.com