Specify correct Ethernet phy for RPI-B

Correct a typo in the RPI-B ethernet config - the RPi-B includes a
SMC LAN9512 USB bridge and Ethernet 10/100 NIC/phy. The phy part of
this is supported by smscphy.

Tested On: RPi1 Model B

Approved by: grog, jhb (mentors)
MFC after: 3 days