PCI: designware: Add irq_create_mapping()

Without irq_create_mapping(), the correct IRQ number cannot be
provided.  In this case, it makes problems such as NULL dereference.
Thus, irq_create_mapping() should be added for MSI.

Suggested-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Pratyush Anand <pratyush.anand@st.com>
Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
diff --git a/drivers/pci/host/pcie-designware.h b/drivers/pci/host/pcie-designware.h
index 890c2ce..c15379b 100644
--- a/drivers/pci/host/pcie-designware.h
+++ b/drivers/pci/host/pcie-designware.h
@@ -50,7 +50,7 @@
 	u32			lanes;
 	struct pcie_host_ops	*ops;
 	int			msi_irq;
-	int			msi_irq_start;
+	struct irq_domain	*irq_domain;
 	unsigned long		msi_data;
 	DECLARE_BITMAP(msi_irq_in_use, MAX_MSI_IRQS);
 };