PCI: pciehp: Remove error checks when accessing PCIe Capability

There's not much point in checking the return value from every config space
access because the only likely errors are design-time things like unaligned
accesses or invalid register numbers.  The checking clutters the code
significantly, so this patch removes it.

No functional change.

Reference: http://lkml.kernel.org/r/CA+55aFzP4xEbcNmZ+MS0SQ3LrULzSq+dBiT_X9U-bPpR-Ukgrw@mail.gmail.com
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>