net: hifemac: make some functions static

They are not required to be global, make them static.

Signed-off-by: Yang Xiwen <forbidden405@outlook.com>
diff --git a/drivers/net/hifemac.c b/drivers/net/hifemac.c
index d24023e..90cc247 100644
--- a/drivers/net/hifemac.c
+++ b/drivers/net/hifemac.c
@@ -418,7 +418,7 @@
 	}
 }
 
-int hisi_femac_of_to_plat(struct udevice *dev)
+static int hisi_femac_of_to_plat(struct udevice *dev)
 {
 	int ret, i;
 	struct hisi_femac_priv *priv = dev_get_priv(dev);
@@ -553,7 +553,7 @@
 	return 0;
 }
 
-int hisi_femac_probe(struct udevice *dev)
+static int hisi_femac_probe(struct udevice *dev)
 {
 	struct hisi_femac_priv *priv = dev_get_priv(dev);
 	int ret, i;