bpf, x86/arm64: remove useless checks on prog

There is never such a situation, where bpf_int_jit_compile() is
called with either prog as NULL or len as 0, so the tests are
unnecessary and confusing as people would just copy them. s390
doesn't have them, so no change is needed there.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>