Check return of pci_enable_device in vortex_up().

Also modify vortex_up to return error to callers. Handle failure of
vortex_up in vortex_open and vortex_resume.
Signed-off-by: NMark Hindley <mark@hindley.org.uk>
Signed-off-by: NJeff Garzik <jeff@garzik.org>