Blackfin: bf518f-ezbrd: fix dsa resources

On bf518-ezbrd with DSA Ethernet switch enabled, on chip MAC is
connecting to phy at address 3.  If allowing the netdevice framework to
probe both 3 phys of the switch when registering MAC phy, phy at address
1 is checked for link active status other than phy at address 3.  If
connecting a cable to port 2 and leave port 1 open, link status in phy
2 and 3 are online, while that in phy 1 is offline.  So, the phy layer
sets wrong offline status to net device on port 3.  In this case, no data
can be transferred via ethernet port 2.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>