i825xx: znet: fix compiler warnings when building a 64-bit kernel

When building 64-bit kernel with this driver we get following warnings from
the compiler:

drivers/net/ethernet/i825xx/znet.c: In function ‘hardware_init’:
drivers/net/ethernet/i825xx/znet.c:863:29: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
drivers/net/ethernet/i825xx/znet.c:870:29: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]

Fix these by calling isa_virt_to_bus() before passing the pointers to
set_dma_addr().

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>