drivers/net/cxgb3: fix sparse warnings: fix signedness

Fix this sparse warning:
  drivers/net/cxgb3/ael1002.c:1010:60: warning: incorrect type in argument 4 (different signedness)

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Acked-by: Divy Le Ray <divy@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>