Input: tsc2007 - rename function tsc2007_calculate_pressure

Rename tsc2007_calculate_pressure to tsc2007_calculate_resistance because
that is what it does.

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>