mips/pci: remove redundant ret variable

Return value from rt3883_pci_r32() directly instead
of taking this in another redundant variable.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Minghao Chi <chi.minghao@zte.com.cn>
Signed-off-by: CGEL ZTE <cgel.zte@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>