irqchip/loongson-eiointc: Use correct struct type in eiointc_domain_alloc()

eiointc_domain_alloc() uses struct eiointc, which is not defined, for a
pointer. Older compilers treat that as a forward declaration and due to
assignment of a void pointer there is no warning emitted. As the variable
is then handed in as a void pointer argument to irq_domain_set_info() the
code is functional.

Use struct eiointc_priv instead.

[ tglx: Rewrote changelog ]

Fixes: dd281e1a ("irqchip: Add Loongson Extended I/O interrupt controller support")
Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Huacai Chen <chenhuacai@loongson.cn>
Link: https://lore.kernel.org/r/20240130082722.2912576-2-maobibo@loongson.cn