ir3: use physical cfg in helper_sched

We used the logical cfg in helper_sched under the assumption that (eq) only kills active helpers. This could lead to something like this:

br p0.x, else
sam
(eq)nop
jump end
else:
sam
end:

It turns out this is not correct: (eq) kills all helpers so the snippet above could produce wrong results.

To fix this, simply switch from using the logical cfg in helper_sched to using the physical cfg.