MIPS: TXx9: Do PCI error checks on own line

Instead of if conditions with line splits, use the usual error handling
pattern with a separate variable to improve readability.

The second check can use reverse logic which reduces indentation level.

No functional changes intended.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>