genirq/msi: Check for the presence of an irq domain when validating msi_ctrl

For architectures such as s390 and powerpc that do not use
irq domains for MSIs, dev->msi.domain is always NULL, so
the per-device, per-bus MSI domain is also guaranteed to
be NULL.

So checking one without checking the other is bound to result
in a splat, followed by a memory leak as we don't free the MSI
descriptors.

Add the missing check.
Reported-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/e570e70d-19bc-101b-0481-ff9a3cab3504@linux.ibm.com

kernel/irq/msi.c

@@ -165,7 +165,8 @@ static bool msi_ctrl_valid(struct device *dev, struct msi_ctrl *ctrl)
 	unsigned int hwsize;
 
 	if (WARN_ON_ONCE(ctrl->domid >= MSI_MAX_DEVICE_IRQDOMAINS ||
-			 !dev->msi.data->__domains[ctrl->domid].domain))
+			 (dev->msi.domain &&
+			  !dev->msi.data->__domains[ctrl->domid].domain)))
 		return false;
 
 	hwsize = msi_domain_get_hwsize(dev, ctrl->domid);