macintosh/via-pmu: Don't clear shift register interrupt flag twice

The shift register interrupt flag gets cleared in via_pmu_interrupt()
and once again in pmu_sr_intr(). Fix this theoretical race condition.
Tested-by: NStan Johnson <userm57@yahoo.com>
Signed-off-by: NFinn Thain <fthain@telegraphics.com.au>
Reviewed-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>

drivers/macintosh/via-pmu.c

@@ -1421,7 +1421,6 @@ pmu_sr_intr(void)
 
 	if (in_8(&via[B]) & TREQ) {
 		printk(KERN_ERR "PMU: spurious SR intr (%x)\n", in_8(&via[B]));
-		out_8(&via[IFR], SR_INT);
 		return NULL;
 	}
 	/* The ack may not yet be low when we get the interrupt */