iwlegacy: avoid warning about missing braces

gcc-6 warns about code in il3945_hw_txq_ctx_free() being
somewhat ambiguous:

drivers/net/wireless/intel/iwlegacy/3945.c:1022:5: warning: suggest explicit braces to avoid ambiguous 'else' [-Wparentheses]

This adds a set of curly braces to avoid the warning.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/intel/iwlegacy/3945.c

@@ -1019,12 +1019,13 @@ il3945_hw_txq_ctx_free(struct il_priv *il)
 	int txq_id;
 
 	/* Tx queues */
-	if (il->txq)
+	if (il->txq) {
 		for (txq_id = 0; txq_id < il->hw_params.max_txq_num; txq_id++)
 			if (txq_id == IL39_CMD_QUEUE_NUM)
 				il_cmd_queue_free(il);
 			else
 				il_tx_queue_free(il, txq_id);
+	}
 
 	/* free tx queue structure */
 	il_free_txq_mem(il);