82596: free resources on error

IRQ 56 was not freed anywhere (neither in i596_open() on error nor in
i596_close()), rx_bufs were not freed if init_i596_mem() fails,
netif_stop_queue() was not called.

Signed-off-by: Kulikov Vasiliy <segooon@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>