rndis_wlan: add missing range check for power_output modparam

Range check for power_output were missing.

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/rndis_wlan.c b/drivers/net/wireless/rndis_wlan.c
index ac56f8d..18c9931 100644
--- a/drivers/net/wireless/rndis_wlan.c
+++ b/drivers/net/wireless/rndis_wlan.c
@@ -2470,6 +2470,11 @@
 	else if (priv->param_power_save > 2)
 		priv->param_power_save = 2;
 
+	if (priv->param_power_output < 0)
+		priv->param_power_output = 0;
+	else if (priv->param_power_output > 3)
+		priv->param_power_output = 3;
+
 	if (priv->param_roamtrigger < -80)
 		priv->param_roamtrigger = -80;
 	else if (priv->param_roamtrigger > -60)