irqchip/gicv3-its: Remove an unused argument 'node_name'

No references to argument 'node_name' after modifying pr_xxx()
messages to include ITS base address instead of 'node_name'.

Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>