MIPS: TXx9: Use PCI_SET_ERROR_RESPONSE()

Instead of literal, PCI error value should be set with
PCI_SET_ERROR_RESPONSE(). Use it in tx4927_pci_config_read().

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Sergio Paracuellos <sergio.paracuellos@gmal.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>