perf/arm-cmn: Initialise cmn->cpu earlier

perf/arm-cmn: Initialise cmn->cpu earlier

For all the complexity of handling affinity for CPU hotplug, what we've
apparently managed to overlook is that arm_cmn_init_irqs() has in fact
always been setting the *initial* affinity of all IRQs to CPU 0, not the
CPU we subsequently choose for event scheduling. Oh dear.

Cc: stable@vger.kernel.org
Fixes: 0ba64770a2f2 ("perf: Add Arm CMN-600 PMU driver")
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Ilkka Koskinen <ilkka@os.amperecomputing.com>
Link: https://lore.kernel.org/r/b12fccba6b5b4d2674944f59e4daad91cd63420b.1747069914.git.robin.murphy@arm.com
Signed-off-by: Will Deacon <will@kernel.org>