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

For cores less than 4, eg, loongson2k1000 with 2 cores, the
of_property_match_string() may return with an error value,
which causes that liointc could not work. At least isr0 is
what should be checked like previous commit b2c4c39
("irqchip/loongson-liointc: irqchip add 2.0 version") did.

Fixes: 0858ed0 ("irqchip/loongson-liointc: Add ACPI init support")
Signed-off-by: Liu Peibao <liupeibao@loongson.cn>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221104110712.23300-1-liupeibao@loongson.cn

drivers/irqchip/irq-loongson-liointc.c

@@ -207,10 +207,13 @@ static int liointc_init(phys_addr_t addr, unsigned long size, int revision,
 					"reg-names", core_reg_names[i]);
 
 			if (index < 0)
-				goto out_iounmap;
+				continue;
 
 			priv->core_isr[i] = of_iomap(node, index);
 		}
+
+		if (!priv->core_isr[0])
+			goto out_iounmap;
 	}
 
 	/* Setup IRQ domain */