net: of_get_phy_mode: Change API to solve int/unit warnings

Before this change of_get_phy_mode() returned an enum,
phy_interface_t. On error, -ENODEV etc, is returned. If the result of
the function is stored in a variable of type phy_interface_t, and the
compiler has decided to represent this as an unsigned int, comparision
with -ENODEV etc, is a signed vs unsigned comparision.

Fix this problem by changing the API. Make the function return an
error, or 0 on success, and pass a pointer, of type phy_interface_t,
where the phy mode should be stored.

v2:
Return with *interface set to PHY_INTERFACE_MODE_NA on error.
Add error checks to all users of of_get_phy_mode()
Fixup a few reverse christmas tree errors
Fixup a few slightly malformed reverse christmas trees

v3:
Fix 0-day reported errors.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/dsa/bcm_sf2.c b/drivers/net/dsa/bcm_sf2.c
index 9add84c..67125a5 100644
--- a/drivers/net/dsa/bcm_sf2.c
+++ b/drivers/net/dsa/bcm_sf2.c
@@ -381,8 +381,9 @@ static void bcm_sf2_identify_ports(struct bcm_sf2_priv *priv,
 				   struct device_node *dn)
 {
 	struct device_node *port;
-	int mode;
 	unsigned int port_num;
+	phy_interface_t mode;
+	int err;
 
 	priv->moca_port = -1;
 
@@ -395,8 +396,8 @@ static void bcm_sf2_identify_ports(struct bcm_sf2_priv *priv,
 		 * has completed, since they might be turned off at that
 		 * time
 		 */
-		mode = of_get_phy_mode(port);
-		if (mode < 0)
+		err = of_get_phy_mode(port, &mode);
+		if (err)
 			continue;
 
 		if (mode == PHY_INTERFACE_MODE_INTERNAL)