MIPS: SGI-IP27: fix -Wunused-variable in arch_init_irq()

MIPS: SGI-IP27: fix -Wunused-variable in arch_init_irq()

Commit 40e20fbccfb722f21 (MIPS: SGI-IP27: micro-optimize arch_init_irq())
replaced a for-loop iteration with bitmap_set() calls, but didn't remove
an iteration variable.

Fixes: 40e20fbccfb722f21 (MIPS: SGI-IP27: micro-optimize arch_init_irq())
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202404161933.izfqZ32k-lkp@intel.com/
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>