Add missing in_8() accessors to init_pmu() and pmu_sr_intr().

This fixes several sparse warnings:
drivers/macintosh/via-pmu.c:536:29: warning: dereference of noderef expression
drivers/macintosh/via-pmu.c:537:33: warning: dereference of noderef expression
drivers/macintosh/via-pmu.c:1455:17: warning: dereference of noderef expression
drivers/macintosh/via-pmu.c:1456:69: warning: dereference of noderef expression
Tested-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>