drivers/net/atlx: fix sparse warnings: fix signedness

Impact: While being at it: statics do not need to be initialized with 0.

Fix this sparse warnings:
  drivers/net/atlx/atl1.c:109:1: warning: incorrect type in initializer (different signedness)
  drivers/net/atlx/atl2.c:2870:1: warning: incorrect type in initializer (different signedness)
  drivers/net/atlx/atl2.c:2880:1: warning: incorrect type in initializer (different signedness)
  drivers/net/atlx/atl2.c:2894:1: warning: incorrect type in initializer (different signedness)
  drivers/net/atlx/atl2.c:2904:1: warning: incorrect type in initializer (different signedness)
  drivers/net/atlx/atl2.c:2913:1: warning: incorrect type in initializer (different signedness)

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Acked-by: Jay Cliburn <jcliburn@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>