mmio_addr in r8169 needs to be initialized before use

Maybe that all tp-> initialization should be moved before rtl_init_mac_address call,
but this is enough to get rid of crash in rtl_rar_set due to mmio_addr being uninitialized.
Signed-off-by: Petr Vandrovec <petr@vandrovec.name>
Signed-off-by: David S. Miller <davem@davemloft.net>