[S390] sparse: fix sparse static warnings

Make functions and data static to avoid sparse warnings.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/drivers/s390/net/qeth_l3_main.c b/drivers/s390/net/qeth_l3_main.c
index ce73520..e4c1176 100644
--- a/drivers/s390/net/qeth_l3_main.c
+++ b/drivers/s390/net/qeth_l3_main.c
@@ -1415,7 +1415,7 @@
 	return 0;
 }
 
-int qeth_l3_set_rx_csum(struct qeth_card *card, int on)
+static int qeth_l3_set_rx_csum(struct qeth_card *card, int on)
 {
 	int rc = 0;