test/power: fix low frequency test when turbo enabled

With the intel_pstate driver and turbo enabled, indexing is slightly
different to normal, so to get the test to work properly, enable
turbo at the start.

Fixes: ed7c51a6a680 ("app/test: vm power management")
Cc: stable@dpdk.org

Signed-off-by: David Hunt <david.hunt@intel.com>

app/test/test_power_cpufreq.c

@@ -249,6 +249,8 @@ check_power_freq_down(void)
 {
 	int ret;
 
+	rte_power_freq_enable_turbo(TEST_POWER_LCORE_ID);
+
 	/* test with an invalid lcore id */
 	ret = rte_power_freq_down(TEST_POWER_LCORE_INVALID);
 	if (ret >= 0) {