gladevcp: fix velocity DRO row position on non-lathes

[grandixximo]

hal_gremlin's dro_format computes where to insert the Vel row in the DRO offsets column, and the lathe test guarding that index referenced the bound method rather than calling it:

if self.is_lathe:
    pos +=1

A bound method is always truthy, so every machine got the lathe offset. On a mill the Vel row was inserted one slot too low, below the blank separator that precedes the G5x offset block, instead of directly under the axis rows.

XYZ mill, before:

      X:    1.000
      Y:    1.000
      Z:    1.000

    Vel:   12.500
  G53 X:    0.000  G92 X:    0.000

after:

      X:    1.000
      Y:    1.000
      Z:    1.000
    Vel:   12.500

  G53 X:    0.000  G92 X:    0.000

Lathe output is unchanged. There the blanked X slot plus the inserted Rad/Dia row is exactly what the extra +1 accounts for, so the index lands in the same place before and after.

I checked the rest of the tree for the same pattern; this was the only paren-less self.is_lathe reference.