According to available DSDT dump from Asus machine, there is the only one
instance of the WMI GUID 97845ED0-4E6D-11DE-8A39-0800200C9A66 and so it is
0x0. Moreover corresponding method WMBC does not check Arg0 (instance
number) at all.

DSDT dump is available at:
https://lwn.net/Articles/391249/

_WDG dump:
0xD0, 0x5E, 0x84, 0x97, 0x6D, 0x4E, 0xDE, 0x11, 0x8A, 0x39, 0x08,
0x00, 0x20, 0x0C, 0x9A, 0x66,
0x42, 0x43,    // Object ID "BC" = method "WMBC"
0x01,          // Instance count
0x02,          // Flags
Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>