macintosh/adb-iop: Correct comment text

This patch improves comment style and corrects some misunderstandings
in the text.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Tested-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/996f835d2f3d90baaaf9ee954e252d06e8886c6f.1590880623.git.fthain@telegraphics.com.au