net/dsa/dsa.c: remove unnecessary null test before kfree

Fix checkpatch warning:
WARNING: kfree(NULL) is safe this check is probably not required

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: netdev@vger.kernel.org
Cc: Joe Perches <joe@perches.com>
Signed-off-by: NFabian Frederick <fabf@skynet.be>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/dsa/dsa.c

@@ -351,8 +351,7 @@ static void dsa_of_free_platform_data(struct dsa_platform_data *pd)
 	for (i = 0; i < pd->nr_chips; i++) {
 		port_index = 0;
 		while (port_index < DSA_MAX_PORTS) {
-			if (pd->chip[i].port_names[port_index])
-				kfree(pd->chip[i].port_names[port_index]);
+			kfree(pd->chip[i].port_names[port_index]);
 			port_index++;
 		}
 		kfree(pd->chip[i].rtable);