rndis_wlan: use power save only for BCM4320b

BCM4320a breaks when enabling power save (bug 29732). So disable power save
for anything but BCM4320b that is known to work.
Signed-off-by: NJussi Kivilinna <jussi.kivilinna@mbnet.fi>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rndis_wlan.c

@@ -2597,6 +2597,9 @@ static int rndis_set_power_mgmt(struct wiphy *wiphy, struct net_device *dev,
 	__le32 mode;
 	int ret;
 
+	if (priv->device_type != RNDIS_BCM4320B)
+		return -ENOTSUPP;
+
 	netdev_dbg(usbdev->net, "%s(): %s, %d\n", __func__,
 				enabled ? "enabled" : "disabled",
 				timeout);