MIPS: OCTEON: fix unreachable code in octeon_irq_init_ciu

The type of 'r' in octeon_irq_init_ciu is 'unsigned int', so 'r < 0'
can't be true.

Fix this by change the type of 'r' and 'i' from 'unsigned int'
to 'int'. As 'i' won't be negative, this change works.

Fixes: 99fbc70f

 ("MIPS: Octeon: irq: Alloc desc before configuring IRQ")
Signed-off-by: Menglong Dong <dong.menglong@zte.com.cn>
Reviewed-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>