net: phy: the NC-SI phy device do not require mdio bus

As with fixed-link phy device, the NC-SI phy devive does not
require an mdio bus. So, a condition is added to check the
NC-SI phy id to avoid accessing the bus pointer that is NULL.

Signed-off-by: Jacky Chou <jacky_chou@aspeedtech.com>
diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
index f39ca94..9cec04a 100644
--- a/drivers/net/phy/phy.c
+++ b/drivers/net/phy/phy.c
@@ -566,7 +566,8 @@
 		return NULL;
 	}
 
-	if (addr >= 0 && addr < PHY_MAX_ADDR && phy_id != PHY_FIXED_ID)
+	if (addr >= 0 && addr < PHY_MAX_ADDR && phy_id != PHY_FIXED_ID &&
+	    phy_id != PHY_NCSI_ID)
 		bus->phymap[addr] = dev;
 
 	return dev;