irqchip/ls-extirq: Fix endianness detection

parent is the interrupt parent, not the parent of node. Use
node->parent. This fixes endianness detection on big-endian platforms.

Fixes: 1b00adce ("irqchip/ls-extirq: Fix invalid wait context by avoiding to use regmap")
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221201212807.616191-1-sean.anderson@seco.com