powerpc/fsl-msi: use a different lockclass for the cascade interrupt

lockdep thinks that it might deadlock because it grabs a lock of the
same class while calling the generic_irq_handler(). This annotation will
inform lockdep that it will not.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

arch/powerpc/sysdev/fsl_msi.c

@@ -333,6 +333,8 @@ static int fsl_of_msi_remove(struct platform_device *ofdev)
 	return 0;
 }
 
+static struct lock_class_key fsl_msi_irq_class;
+
 static int fsl_msi_setup_hwirq(struct fsl_msi *msi, struct platform_device *dev,
 			       int offset, int irq_index)
 {
@@ -351,7 +353,7 @@ static int fsl_msi_setup_hwirq(struct fsl_msi *msi, struct platform_device *dev,
 		dev_err(&dev->dev, "No memory for MSI cascade data\n");
 		return -ENOMEM;
 	}
-
+	irq_set_lockdep_class(virt_msir, &fsl_msi_irq_class);
 	msi->msi_virqs[irq_index] = virt_msir;
 	cascade_data->index = offset;
 	cascade_data->msi_data = msi;