xtensa: fix xtensa_pmu_setup prototype

Fix the following build error in configurations with
CONFIG_XTENSA_VARIANT_HAVE_PERF_EVENTS=y:

  arch/xtensa/kernel/perf_event.c:420:29: error: passing argument 3 of
  ‘cpuhp_setup_state’ from incompatible pointer type

Cc: stable@vger.kernel.org
Fixes: 25a77b55 ("xtensa/perf: Convert the hotplug notifier to state machine callbacks")
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/kernel/perf_event.c

@@ -399,7 +399,7 @@ static struct pmu xtensa_pmu = {
 	.read = xtensa_pmu_read,
 };
 
-static int xtensa_pmu_setup(int cpu)
+static int xtensa_pmu_setup(unsigned int cpu)
 {
 	unsigned i;