HID: wacom: generic: Use generic codepath terminology in wacom_wac_pen_report

The terminology used to describe the various degrees of pen proximity
within the wacom_wac_pen_report function does not match that used elsewhere
in the generic codepath. Specifically, the names of the variables "prox"
and "range" were inspired by the non-generic codepaths. To make the generic
codepath internally consistent, replace these terms with "range" and "sense"
respectively.

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