Rockchip: Add some debug assertions in the PMU driver

This patch adds some debug assertions ensuring that array indices
are within the bounds of the array.

Change-Id: I96ee81d14834c1e92cdfb7e60b49995cdacfd93a
diff --git a/plat/rockchip/rk3368/drivers/pmu/pmu.c b/plat/rockchip/rk3368/drivers/pmu/pmu.c
index 50e2bf8..53d333b 100644
--- a/plat/rockchip/rk3368/drivers/pmu/pmu.c
+++ b/plat/rockchip/rk3368/drivers/pmu/pmu.c
@@ -349,6 +349,7 @@
 	cpus_id_power_domain(cluster, cpu, pmu_pd_off, CKECK_WFEI_MSK);
 
 	cpuon_id = (cluster * PLATFORM_CLUSTER0_CORE_COUNT) + cpu;
+	assert(cpuon_id < PLATFORM_CORE_COUNT);
 	assert(cpuson_flags[cpuon_id] == 0);
 	cpuson_flags[cpuon_id] = PMU_CPU_HOTPLUG;
 	cpuson_entry_point[cpuon_id] = entrypoint;