Fix typo in G34 logic

[Evgeny-SPB]

Description

After commit 832cb7e logic in Z-Probing is broken.

In this Function we use downward / upward stepper sequence for probing

// iteration odd/even --> downward / upward stepper sequence
const uint8_t iprobe = (iteration & 1) ? G34_PROBE_COUNT - 1 - i : i;

In commit 832cb7e there was a name change of a few variables, and a typo occurred.
BEFORE:

const float z_probed_height = probe_at_point(z_auto_align_pos[zstepper], raise_after, 0, true);
z_measured[zstepper] = z_probed_height + Z_CLEARANCE_BETWEEN_PROBES;

AFTER:

const float z_probed_height = probe_at_point(z_auto_align_pos[i], raise_after, 0, true);
z_measured[iprobe] = z_probed_height + Z_CLEARANCE_BETWEEN_PROBES;

So we measure height in position "[i]" and put this measurement in "[iprobe]" position.

On first iteration (iteration = 0), everything is working as expected, because i = iprobe, on the next iteration i != iprobe, so G34 is not working and gives odd results.

Benefits

G34 works as expected

Related Issues

No

[sjasonsmith]

This seems to be a minor error that was introduced during merging. The change looks right to me.

When I tested post-merge I must not have noticed it probed the points in the same order on all iterations.

I may have only re-tested post-merge with known stepper positions, so even if iteration #2 corrected in the wrong direction, my second iteration correction is sub-millimeter so I wouldn't have really noticed.

I also don't have this triple-Z printer at home, so I've only used it a handful of times since this change went in.