ARM: perf: remove mysterious compiler barrier

There's a rather strange compiler barrier in the PMU disabling code
which was presumably placed there by aliens. There's no valid reason for
the barrier and one can only suspect that it's up to no good.

This patch removes it before it has a chance to spread.
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm/kernel/perf_event.c

@@ -223,7 +223,6 @@ armpmu_stop(struct perf_event *event, int flags)
 	 */
 	if (!(hwc->state & PERF_HES_STOPPED)) {
 		armpmu->disable(hwc, hwc->idx);
-		barrier(); /* why? */
 		armpmu_event_update(event, hwc, hwc->idx);
 		hwc->state |= PERF_HES_STOPPED | PERF_HES_UPTODATE;
 	}