Input: stmpe-ts - restore kerneldoc

commit e4b88e19
"Input: stmpe-ts - enforce device tree only mode"
removed platform data but accidentally stripped away useful
kerneldoc, so reintroduce it.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>