dl2k: Handle memory allocation errors in alloc_list

If memory allocation fails in alloc_list(), free the already allocated
memory and return -ENOMEM. In rio_open(), call alloc_list() first and
abort if it fails. Move HW access (set RFDListPtr) out ot alloc_list().

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: David S. Miller <davem@davemloft.net>