acpi video device enumeration: fix incorrect device list allocation

It didn't allocate space for the final terminating entry,
which caused it to overwrite the next slab entry, which in turn
sometimes ended up being a slab array cache pointer. End result:
total slab cache corruption at a random time afterwards. Very
nasty.

drivers/acpi/video.c

@@ -1524,7 +1524,7 @@ static int acpi_video_device_enumerate(struct acpi_video_bus *video)
 		dod->package.count));
 
 	active_device_list= kmalloc(
- 		dod->package.count*sizeof(struct acpi_video_enumerated_device),
+ 		(1+dod->package.count)*sizeof(struct acpi_video_enumerated_device),
 	       	GFP_KERNEL);
 
 	if (!active_device_list) {