Vtx ready fix

[RomanLut]

Fixed: vtxSAIsReady() returns true before VTX is initialized
Fixed: vtxSAGetPowerIndex() should not try to convert power index for SA 1.0 devices

Symptoms:
If VTX is not connected and can not be initialized, OSD shows power level (powerIndexLetter) "/"
(which is "0" + -1 )

[RomanLut]

I beleave I have to add more information here.
This fix with along with #6458 were required for new AKK AIO camera to work for me.
vtxSAIsReady() returns true before camera is initialized due to bug in implementation.

[stale]

This issue / pull request has been automatically marked as stale because it has not had any activity in 60 days. The resources of the INAV team are limited, and so we are asking for your help.
This issue / pull request will be closed if no further activity occurs within two weeks.

[stale]

This issue / pull request has been automatically marked as stale because it has not had any activity in 60 days. The resources of the INAV team are limited, and so we are asking for your help.
This issue / pull request will be closed if no further activity occurs within two weeks.