typhoon: fix incorrect use of smp_wmb()

The typhoon driver was incorrectly using smp_wmb() to order memory
accesses against IO to the NIC in a few instances. Use wmb() instead,
which is required to actually order between memory types.

Signed-off-by: David Dillow <dave@thedillows.org>
Signed-off-by: David S. Miller <davem@davemloft.net>