Using parent->regs[] when propagating REG_LIVE_READ for spilled regs
doesn't work since parent->regs[] denote the set of normal registers
but not spilled ones. Propagate to the correct regs.

Fixes: dc503a8a ("bpf/verifier: track liveness for pruning")
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NEdward Cree <ecree@solarflare.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>