Fixes the following W=1 kernel build warning(s):

 drivers/input/misc/ab8500-ponkey.c:32: warning: Function parameter or member 'idev' not described in 'ab8500_ponkey'
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201104162427.2984742-5-lee.jones@linaro.orgSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>