cpufreq: conservative: fix requested_freq reduction issue

When decreasing frequency, requested_freq may be less than
freq_target, So requested_freq minus freq_target may be negative,
But reqested_freq's unit is unsigned int, then the negative result
will be one larger interger which may be even higher than
requested_freq.

This patch is to fix such issue. when result becomes negative,
set requested_freq as the min value of policy.

Signed-off-by: Xiaoguang Chen <chenxg@marvell.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/cpufreq_conservative.c

@@ -80,13 +80,18 @@ static void cs_check_cpu(int cpu, unsigned int load)
 
 	/* Check for frequency decrease */
 	if (load < cs_tuners->down_threshold) {
+		unsigned int freq_target;
 		/*
 		 * if we cannot reduce the frequency anymore, break out early
 		 */
 		if (policy->cur == policy->min)
 			return;
 
-		dbs_info->requested_freq -= get_freq_target(cs_tuners, policy);
+		freq_target = get_freq_target(cs_tuners, policy);
+		if (dbs_info->requested_freq > freq_target)
+			dbs_info->requested_freq -= freq_target;
+		else
+			dbs_info->requested_freq = policy->min;
 
 		__cpufreq_driver_target(policy, dbs_info->requested_freq,
 				CPUFREQ_RELATION_L);