bpf: fix liveness propagation to parent in spilled stack slots

bpf: fix liveness propagation to parent in spilled stack slots

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: dc503a8ad984 ("bpf/verifier: track liveness for pruning")
Reported-by: Dan Carpenter <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Acked-by: Edward Cree <[email protected]>
Signed-off-by: David S. Miller <[email protected]>