HID: i2c-hid: acpi: Move GUID out of function and described it

Move static GUID variable out of the function and add a comment
how it looks like in the human readable representation.

While at it, include uuid.h since the guid_t type is defined in it.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>