tools, bpf_asm: Exit non-zero on errors

... so callers can correctly detect failure.

Signed-off-by: Ian Denhardt <ian@zenhack.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/b0bea780bc292f29e7b389dd062f20adc2a2d634.1614201868.git.ian@zenhack.net