arm64: perf: Correct the event index in sysfs

When PMU event ID is equal or greater than 0x4000, it will be reduced
by 0x4000 and it is not the raw number in the sysfs. Let's correct it
and obtain the raw event ID.

Before this patch:
cat /sys/bus/event_source/devices/armv8_pmuv3_0/events/sample_feed
event=0x001
After this patch:
cat /sys/bus/event_source/devices/armv8_pmuv3_0/events/sample_feed
event=0x4001

Signed-off-by: Shaokun Zhang <zhangshaokun@hisilicon.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/1592487344-30555-3-git-send-email-zhangshaokun@hisilicon.com
[will: fixed formatting of 'if' condition]
Signed-off-by: Will Deacon <will@kernel.org>