PCI: designware-plat: Drop unnecessary root_bus_nr setting

Function dw_pcie_host_init() already initializes the root_bus_nr field
of 'struct pcie_port', so the -1 assignment prior to calling
dw_pcie_host_init() in platform specific driver is not really needed.
Drop it.
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Cc: Joao Pinto <Joao.Pinto@synopsys.com>

drivers/pci/controller/dwc/pcie-designware-plat.c

@@ -118,7 +118,6 @@ static int dw_plat_add_pcie_port(struct dw_plat_pcie *dw_plat_pcie,
 			return pp->msi_irq;
 	}
 
-	pp->root_bus_nr = -1;
 	pp->ops = &dw_plat_pcie_host_ops;
 
 	ret = dw_pcie_host_init(pp);