HID: wacom: Simplify 'wacom_update_name'

A little bit of cleanup work for 'wacom_update_name' to make it easier on
the eyes. Creates a temporary 'name' variable on which we'll perform our
edits. Once the name is in its final form, it will be copied (with
appropriate suffix) to 'wacom_wac->name' and 'wacom_wac->pad_name'.

Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>