net/ethoc: don't mix virtual and physical addresses

Addresses used in buffer descriptors and passed in platform data or
device tree are physical. Addresses used by CPU to access packet data
and registers are virtual. Don't mix these addresses and use virt_to_phys
for translation.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>