ns83820: Avoid bad pointer deref in ns83820_init_one().

In drivers/net/ns83820.c::ns83820_init_one() we dynamically allocate
memory via alloc_etherdev(). We then call PRIV() on the returned storage
which is 'return netdev_priv()'. netdev_priv() takes the pointer it is
passed and adds 'ALIGN(sizeof(struct net_device), NETDEV_ALIGN)' to it and
returns it. Then we test the resulting pointer for NULL, which it is
unlikely to be at this point, and later dereference it. This will go bad
if alloc_etherdev() actually returned NULL.

This patch reworks the code slightly so that we test for a NULL pointer
(and return -ENOMEM) directly after calling alloc_etherdev().

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>
Signed-off-by: David S. Miller <davem@davemloft.net>