[ATM] nicstar: Fix a bogus casting warning

Not enough to make Nicstar 64bit friendly but got squashed in passing so might
as well be applied

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>