irqchip/mbigen: Checking for IS_ERR() instead of NULL

of_platform_device_create() returns NULL on error, it never returns
error pointers.

Fixes: ed2a1002d25c ('irqchip/mbigen: Handle multiple device nodes in a mbigen module')
Acked-by: Marc Zyngier <[e-mail]>
Signed-off-by: Dan Carpenter <[e-mail]>
Signed-off-by: Marc Zyngier <[e-mail]>

drivers/irqchip/irq-mbigen.c

···
 
 		parent = platform_bus_type.dev_root;
 		child = of_platform_device_create(np, NULL, parent);
-		if (IS_ERR(child))
-			return PTR_ERR(child);
+		if (!child)
+			return -ENOMEM;
 
 		if (of_property_read_u32(child->dev.of_node, "num-pins",
 					 &num_pins) < 0) {