Revert "powerpc/perf: Use pmc_overflow() to detect rolled back events"

This reverts commit 81331211.

This revert was requested by the author of the patch as it seems
to cause system hangs with some low frequency events

arch/powerpc/perf/core-book3s.c

@@ -1463,7 +1463,7 @@ static void perf_event_interrupt(struct pt_regs *regs)
 		if (!event->hw.idx || is_limited_pmc(event->hw.idx))
 			continue;
 		val = read_pmc(event->hw.idx);
-		if (pmc_overflow(val)) {
+		if ((int)val < 0) {
 			/* event has overflowed */
 			found = 1;
 			record_and_restart(event, val, regs);