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>
diff --git a/net/wireless/reg.c b/net/wireless/reg.c
index 85c9034..bd0a16c 100644
--- a/net/wireless/reg.c
+++ b/net/wireless/reg.c
@@ -380,7 +380,8 @@
 
 	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;