net: fix phy_string_for_interface

commit ffb0f6f4 ("treewide: Rename PHY_INTERFACE_MODE_NONE to
PHY_INTERFACE_MODE_NA") broke the phy_string_for_interface function.
Fix it.

Fixes ffb0f6f4 ("treewide: Rename PHY_INTERFACE_MODE_NONE to PHY_INTERFACE_MODE_NA")
Signed-off-by: NTim Harvey <tharvey@gateworks.com>
Cc: Marek Behún <marek.behun@nic.cz>
Cc: Stefan Roese <sr@denx.de>
Cc: Ramon Fried <rfried.dev@gmail.com>
Cc: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: NStefan Roese <sr@denx.de>
Reviewed-by: NMarek Behún <marek.behun@nic.cz>
Reviewed-by: NRamon Fried <rfried.dev@gmail.com>

include/phy_interface.h

@@ -85,7 +85,7 @@ static const char * const backplane_mode_strings[] = {
 static inline const char *phy_string_for_interface(phy_interface_t i)
 {
 	/* Default to unknown */
-	if (i > PHY_INTERFACE_MODE_NA)
+	if (i >= PHY_INTERFACE_MODE_MAX)
 		i = PHY_INTERFACE_MODE_NA;
 
 	return phy_interface_strings[i];