[PATCH] sysfs: (driver/pci) if show/store is missing return -EIO

sysfs: fix drivers/pci so if an attribute does not implement
       show or store method read/write will return -EIO
       instead of 0.

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>