MARI: jaws: positions defined incorrectly

Observed when setting up jaws during MARI migration, on the physical hardware on MARI.

As far as I can tell, the sequence of events is:
- Start galil IOC
- Initially the galil will read the raw position as zero (so the "actual" position is the offset)
- The jaws DB records "get" the current positions
- Some time later, the galil ioc manages to actually read the raw position
- The jaws DB records re-apply the first position they got, resulting in the jaws moving until actual position == offset

Fixing this ticket is required for MARI to be able to use their jaws under IBEX.