Fix this sparse warnings:
  drivers/net/r6040.c:487:31: warning: Using plain integer as NULL pointer
  drivers/net/r6040.c:492:31: warning: Using plain integer as NULL pointer
Signed-off-by: NHannes Eder <hannes@hanneseder.net>
Acked-by: NFlorian Fainelli <florian@openwrt.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>