irqchip/irq-ls1x: Missing error code in ls1x_intc_of_init()

Currently, when irq_domain_add_linear() fails, the error code does not get
set so it returns zero which is wrong. Fix it by setting the appropriate
error code.

Fixes: 9e543e22e204 ("irqchip: Add driver for Loongson-1 interrupt controller")
Signed-off-by: Dan Carpenter <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Reviewed-by: Mukesh Ojha <[e-mail]>
Cc: Marc Zyngier <[e-mail]>
Cc: Jiaxun Yang <[e-mail]>
Cc: Jason Cooper <[e-mail]>
Cc: [e-mail]
Link: https://lkml.kernel.org/r/20190329062136.GQ32613@kadam

drivers/irqchip/irq-ls1x.c

···
 					     NULL);
 	if (!priv->domain) {
 		pr_err("ls1x-irq: cannot add IRQ domain\n");
+		err = -ENOMEM;
 		goto out_iounmap;
 	}