smsc9420: use named constants for pci_power_t values

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/

)

// <smpl>
@@
expression e1,e2;
@@

pci_enable_wake(e1,
- 0
+ PCI_D0
,e2)
// </smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>