cfg80211: test before subtraction on unsigned

freq_diff is unsigned, so test before subtraction
Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/wireless/reg.c

@@ -380,7 +380,8 @@ static bool is_valid_reg_rule(const struct ieee80211_reg_rule *rule)
 
 	freq_diff = freq_range->end_freq_khz - freq_range->start_freq_khz;
 
-	if (freq_diff <= 0 || freq_range->max_bandwidth_khz > freq_diff)
+	if (freq_range->end_freq_khz <= freq_range->start_freq_khz ||
+			freq_range->max_bandwidth_khz > freq_diff)
 		return false;
 
 	return true;