[PATCH] sky2: use standard pci register capabilties for error register

Use the standard pci capability mechanism to access PCI express error
registers, rather than hard coding the offset. Mask off the PCI express
error from ever occuring on non-PCI express systems.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>