irqchip/renesas-irqc: Use proper irq_chip name and parent

The irq_chip .name field should contain the device's class (not
instance) name, while .parent_device should point to the device itself.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>