netxen: fix sparse warnings

Fix following sparse warnings (multiple instances)

warning: restricted degrades to integer
warning: cast to restricted type
warning: incorrect type in argument 3 (different signedness)
warning: context imbalance in 'netxen_nic_hw_write_wx_2M' - different
lock contexts for basic block

Signed-off-by: Dhananjay Phadke <dhananjay@netxen.com>
Signed-off-by: David S. Miller <davem@davemloft.net>