s390/pci: Use PCIBIOS return values in pci_read()/pci_write()

s390/pci: Use PCIBIOS return values in pci_read()/pci_write()

While pci_read() and pci_write() have returned errno values since their
inception with commit cd24834130ac ("s390/pci: base support") other
config accessors in particular pci_generic_config_read() as well as
pci_generic_config_write() return specific error values which are then
converted to errno by pcibios_err_to_errno(). Since latter does handle
the case where the error value already looks like an errno the previous
behavior is unlikely to cause actual issues.

Still, for consistency and in case any caller explicitly checks error
values align pci_read() and pci_write() with the generic accessors.

Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Reviewed-by: Farhan Ali <alifm@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>