ravb: ravb_close() always returns 0

ravb_close() always returns 0, hence the check in ravb_wol_restore() is
pointless (however, we cannot change the prototype of ravb_close() as it
implements the driver's ndo_stop() method).

Found by Linux Verification Center (linuxtesting.org) with the SVACE static
analysis tool.

Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>