irqchip/riscv-aplic: Simplify the initialization code

The initialization code has an is_of_node() check and invokes to_of_node()
for every of_property_*() invocation.

to_of_node() has a is_of_node() check already, so simplify the code by
invoking to_of_node() and checking that for NULL. If not NULL hand in the
node pointer to of_property_*().

The same applies to of_property_*() which fails when invoked with a NULL
node pointer.

[ tglx: Massaged change log ]

Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20240603125652.791601-1-ruanjinjie@huawei.com