irqchip/mips-gic: Use irq_set_chip_handler_name_locked

Use irq_set_handler_name_locked() as it avoids a redundant lookup of
the irq descriptor.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Jason Cooper <jason@lakedaemon.net>