irqchip/loongson-liointc: Fix an error handling path in liointc_init()

All errors lead to the error handling path, except the one dealing
with "reg-names" in DT.

Fix it and release some resources before returning if this test fails.

Fixes: 0858ed03

 ("irqchip/loongson-liointc: Add ACPI init support")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
[maz: fix commit message]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/1a6d74ab70712279023aa7bdbd31bd3aec103bc0.1659382063.git.christophe.jaillet@wanadoo.fr