[ISDN] HiSax hfc_pci: minor cleanups

* trim trailing whitespace
* remove CONFIG_PCI ifdefs, this driver is always PCI (Kconfig enforced)
* remove return statements at the tail of a function
* remove indentation levels by returning an error code immediately.
  Makes the code much more readable, and easier to update to PCI hotplug
  API.

Signed-off-by: Jeff Garzik <jeff@garzik.org>