PCI: imx6: 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>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Cc: Richard Zhu <hongxing.zhu@nxp.com>
Cc: Lucas Stach <l.stach@pengutronix.de>

drivers/pci/controller/dwc/pci-imx6.c

@@ -667,7 +667,6 @@ static int imx6_add_pcie_port(struct imx6_pcie *imx6_pcie,
 		}
 	}
 
-	pp->root_bus_nr = -1;
 	pp->ops = &imx6_pcie_host_ops;
 
 	ret = dw_pcie_host_init(pp);