iwlwifi: error checking for setting tx_power in sysfs

Perform error checking and report failure when setting tx power from
sysfs.
If fail to set the tx power, do not update the local copy, so user will
not see the incorrect tx power in sysfs

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwlwifi/iwl-agn.c

@@ -2477,10 +2477,15 @@ static ssize_t store_tx_power(struct device *d,
 	ret = strict_strtoul(buf, 10, &val);
 	if (ret)
 		IWL_INFO(priv, "%s is not in decimal form.\n", buf);
-	else
-		iwl_set_tx_power(priv, val, false);
-
-	return count;
+	else {
+		ret = iwl_set_tx_power(priv, val, false);
+		if (ret)
+			IWL_ERR(priv, "failed setting tx power (0x%d).\n",
+				ret);
+		else
+			ret = count;
+	}
+	return ret;
 }
 
 static DEVICE_ATTR(tx_power, S_IWUSR | S_IRUGO, show_tx_power, store_tx_power);