HID: huion: Use "tablet" instead of specific model

Use word "tablet" in identifiers and comments instead of referring to specific
Huion tablet model name, as the product ID is used by at least several tablet
models.

Signed-off-by: Nikolai Kondrashov <spbnick@gmail.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>