Add func to get nbr of PMU event counters

Small bugfix to a print in driver

Change-Id: I277a441a9f65c647c338b92af5a908176929102c
diff --git a/src/ethosu_pmu.c b/src/ethosu_pmu.c
index 647f3b0..e11636a 100644
--- a/src/ethosu_pmu.c
+++ b/src/ethosu_pmu.c
@@ -101,6 +101,11 @@
     set_clock_and_power_request(drv, ETHOSU_PMU_REQUEST, ETHOSU_CLOCK_Q_ENABLE, ETHOSU_POWER_Q_ENABLE);
 }
 
+uint32_t ETHOSU_PMU_Get_NumEventCounters(void)
+{
+    return NPU_REG_PMEVCNTR_ARRLEN;
+}
+
 void ETHOSU_PMU_Set_EVTYPER(struct ethosu_driver *drv, uint32_t num, enum ethosu_pmu_event_type type)
 {
     assert(num < ETHOSU_PMU_NCOUNTERS);