ARM: tegra: pcie: 0 -> NULL changes

Fixes:

arch/arm/mach-tegra/pcie.c:465:10: warning: Using plain integer as NULL pointer

Signed-off-by: Olof Johansson <olof@lixom.net>
Acked-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>

arch/arm/mach-tegra/pcie.c

@@ -462,7 +462,7 @@ static struct pci_bus __init *tegra_pcie_scan_bus(int nr,
 	struct tegra_pcie_port *pp;
 
 	if (nr >= tegra_pcie.num_ports)
-		return 0;
+		return NULL;
 
 	pp = tegra_pcie.port + nr;
 	pp->root_bus_nr = sys->busnr;