cpupower: fix how "cpupower frequency-info" interprets latency

the intel-pstate driver does not support the ondemand governor and does not
have a valid value in
/sys/devices/system/cpu/cpu[x]/cpufreq/cpuinfo_transition_latency. The
intel-pstate driver sets cpuinfo_transition_latency to CPUFREQ_ETERNAL (-1),
the value written into cpuinfo_transition_latency is defind as an unsigned
int so checking the read value against max unsigned int will determine if the
value is valid.

Signed-off-by: Jacob Tanenbaum <[e-mail]>
Signed-off-by: Thomas Renninger <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

tools/power/cpupower/utils/cpufreq-info.c

···
 	unsigned long latency = cpufreq_get_transition_latency(cpu);
 
 	printf(_("  maximum transition latency: "));
-	if (!latency) {
-		printf(_(" Cannot determine latency.\n"));
+	if (!latency || latency == UINT_MAX) {
+		printf(_(" Cannot determine or is not supported.\n"));
 		return -EINVAL;
 	}