m68k/mac: Use correct PMU response format

Now that the 68k Mac port has adopted the via-pmu driver, it must decode
the PMU response accordingly otherwise the date and time will be wrong.

Fixes: ebd72227 ("macintosh/via-pmu: Replace via-pmu68k driver with via-pmu driver")
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>