Input: psmouse - rename ps2pp_init() to ps2pp_detect()

This makes Logitech PS2++ protocol implementation consistent with
the naming in other protocols. Also mark the stub as "static inline"

Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Tested-by: Marcin Sochacki <msochacki+kernel@gmail.com>
Tested-by: Till <till2.schaefer@uni-dortmund.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>