[Coco] 64K Coco mode and the MC6883

[Sean Conner]

It was thus said that the Great Arthur Flexser via Coco once stated:
> That is, I think the last part of line 10 should read simply, P=VARPTR(P$)+2
> (the +2 to access the 3rd byte of the 5-byte string descriptor).
> 
> I see no need to add that JMP (126) byte.

  Perhaps I was too cute with the implementation---I copied the method from

	https://subethasoftware.com/2022/09/16/coco-rom-to-ram-64k-test-part-2/

  My actual Coco is in storage, and I currently don't have ready access to
the Coco emulator I was using (xroar) for reasons.

  -spc