m68k/mac: Fix RTC on PMU machines

Copy RTC response bytes correctly on powerbooks and duos. Thanks to Diego
Cousinet who debugged this and provided me with the fix. Tested on
PowerBook 190 and Duo 280c.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Reported-by: Diego Cousinet <diego@pvco.net>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>