smc91c92_cs: fix the problem of "Unable to find hardware address"

smc91c92_cs:
 *cvt_ascii_address returns 0, if success.
 *call free_netdev, if we can't find hardware address.

Signed-off-by: Ken Kawasaki <ken_kawasaki@spring.nifty.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>