drivers/platform/x86/wmi.c: use generic UUID library

Instead of opencoding let's use generic UUID library functions here.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>