ARM: 6865/1: perf: ensure pass through zero is counted on overflow

ARM: 6865/1: perf: ensure pass through zero is counted on overflow

Commit 99605d53 ("ARM: perf: ensure overflows aren't missed due to IRQ
latency") changed the way that event deltas are calculated on overflow
so that we don't miss events when the new count value overtakes the
previous one.

Unfortunately, we forget to count the event that passes through zero so
we end up being off by 1. This patch adds on the correction.

Reported-by: Chris Moore <moore@free.fr>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>