net: dsa: mt7530: make functions mt7530_phy_write static

The function mt7530_phy_write is local to the source and does not need to
be in global scope, so make it static.

Cleans up sparse warnings:
symbol 'mt7530_phy_write' was not declared. Should it be static?
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mt7530.c

@@ -564,7 +564,8 @@ static int mt7530_phy_read(struct dsa_switch *ds, int port, int regnum)
 	return mdiobus_read_nested(priv->bus, port, regnum);
 }
 
-int mt7530_phy_write(struct dsa_switch *ds, int port, int regnum, u16 val)
+static int mt7530_phy_write(struct dsa_switch *ds, int port, int regnum,
+			    u16 val)
 {
 	struct mt7530_priv *priv = ds->priv;