cpupower: Fix sscanf robustness in cpufreq-set

The cpufreq-set tool has a missing length check. This is basically
just correctness but still should get fixed.

One of a set of sscanf problems reported by Jackie Chang

Signed-off-by: Alan Cox <alan@linux.intel.com>
[rjw: Subject]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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

@@ -257,7 +257,7 @@ int cmd_freq_set(int argc, char **argv)
 				print_unknown_arg();
 				return -EINVAL;
 			}
-			if ((sscanf(optarg, "%s", gov)) != 1) {
+			if ((sscanf(optarg, "%19s", gov)) != 1) {
 				print_unknown_arg();
 				return -EINVAL;
 			}