irqchip/irq-msi-lib: Check for NULL ops in msi_lib_irq_domain_select()

The irq_domain passed to msi_lib_irq_domain_select() may not have
msi_parent_ops set. There is a NULL pointer check for it, but unfortunately
there is a dereference of the parent ops pointer before that.

Move the NULL pointer test before the first use of that pointer.

This was found on a MacchiatoBin (Marvell Armada 8K SoC), which uses the
irq-mvebu-sei driver.

Fixes: 72e257c6f058 ("irqchip: Provide irq-msi-lib")
Signed-off-by: Maxime Chevallier <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Link: https://lore.kernel.org/all/[e-mail]
Closes: https://lore.kernel.org/all/[e-mail]/

drivers/irqchip/irq-msi-lib.c

···
 	const struct msi_parent_ops *ops = d->msi_parent_ops;
 	u32 busmask = BIT(bus_token);
 
+	if (!ops)
+		return 0;
+
 	if (fwspec->fwnode != d->fwnode || fwspec->param_count != 0)
 		return 0;
 
···
 	if (bus_token == ops->bus_select_token)
 		return 1;
 
-	return ops && !!(ops->bus_select_mask & busmask);
+	return !!(ops->bus_select_mask & busmask);
 }
 EXPORT_SYMBOL_GPL(msi_lib_irq_domain_select);