netxen: Use kobj_to_dev()

Introduce the use of kobj_to_dev() helper function instead of open
coding it with container_of()

The Coccinelle semantic patch used to make this change is as follows:

//<smpl>
@@
expression a;
symbol kobj;
@@
- container_of(a, struct device, kobj)
+ kobj_to_dev(a)
//</smpl>

Signed-off-by: Amitoj Kaur Chawla <amitoj1606@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>