PCI: dwc: Replace magic number by defines

Replace magic numbers by a self-explained define to ease human
comprehension.

Signed-off-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Jingoo Han <jingoohan1@gmail.com>
Acked-by: Joao Pinto <jpinto@synopsys.com>
diff --git a/drivers/pci/dwc/pcie-designware.h b/drivers/pci/dwc/pcie-designware.h
index fe811db..bee4e25 100644
--- a/drivers/pci/dwc/pcie-designware.h
+++ b/drivers/pci/dwc/pcie-designware.h
@@ -110,6 +110,7 @@
 #define MAX_MSI_IRQS			256
 #define MAX_MSI_IRQS_PER_CTRL		32
 #define MAX_MSI_CTRLS			(MAX_MSI_IRQS / MAX_MSI_IRQS_PER_CTRL)
+#define MSI_REG_CTRL_BLOCK_SIZE		12
 #define MSI_DEF_NUM_VECTORS		32
 
 /* Maximum number of inbound/outbound iATUs */