devicetree: Rename unused parameter to passthru

The actual use of the parameter max is to keep track of PCI bus
number while recursively scanning PCI bridges or PCI-e rootports.

Neither CPU, SMBus, LPC or other static buses are involved in this
enumeration, but the way bridge operations were originally designed
forced to pass this argument thru unrelated functions.

Follow-up removes these once the function prototype gets fixed.

Change-Id: Idbc9c515a362c571a1798bb36972058b309c2774
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/8535
Tested-by: build bot (Jenkins)
Reviewed-by: Timothy Pearson <tpearson@raptorengineeringinc.com>

src/mainboard/emulation/qemu-i440fx/northbridge.c

@@ -241,7 +241,7 @@ static void cpu_bus_init(device_t dev)
 	initialize_cpus(dev->link_list);
 }
 
-static unsigned int cpu_bus_scan(device_t bus, unsigned int max)
+static unsigned int cpu_bus_scan(device_t bus, unsigned int passthru)
 {
 	int max_cpus = fw_cfg_max_cpus();
 	device_t cpu;