HID: wacom: Only report rotation for art pen

The generic routine, wacom_wac_pen_event, turns rotation value 90
degree anti-clockwise before posting the events. This non-zero
event trggers a non-zero ABS_Z event for non art pen tools. However,
HID_DG_TWIST is only supported by art pen.

[jkosina@suse.cz: fix build: add missing brace]
Cc: stable@vger.kernel.org
Signed-off-by: Ping Cheng <ping.cheng@wacom.com>
Reviewed-by: Jason Gerecke <jason.gerecke@wacom.com>
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Hi Jiri,

This is kind of a version 2 of the last one I posted two days ago.
I updated the logic so it has less changed lines: 29 vs 158! Hopefully,
the logic is easier to follow now. Please ignore the last one.

Thank you!
Signed-off-by: Jiri Kosina <jkosina@suse.cz>