net: 7990: Export lance_poll() to modules

If CONFIG_HPLANCE=m and CONFIG_NET_POLL_CONTROLLER=y:

    ERROR: "lance_poll" [drivers/net/ethernet/amd/hplance.ko] undefined!

Add the missing export to fix this.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: David S. Miller <davem@davemloft.net>