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 b2c4c3969fd7
("irqchip/loongson-liointc: irqchip add 2.0 version") did.

Fixes: 0858ed035a85 ("irqchip/loongson-liointc: Add ACPI init support")
Signed-off-by: Liu Peibao <[e-mail]>
Signed-off-by: Marc Zyngier <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/irqchip/irq-loongson-liointc.c

···
 					"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 */