Input: applespi - provide missing struct 'message' descriptions

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

 drivers/input/keyboard/applespi.c:306: warning: Function parameter or member 'keyboard' not described in 'message'
 drivers/input/keyboard/applespi.c:306: warning: Function parameter or member 'touchpad' not described in 'message'
 drivers/input/keyboard/applespi.c:306: warning: Function parameter or member 'tp_info' not described in 'message'
 drivers/input/keyboard/applespi.c:306: warning: Function parameter or member 'tp_info_command' not described in 'message'
 drivers/input/keyboard/applespi.c:306: warning: Function parameter or member 'init_mt_command' not described in 'message'
 drivers/input/keyboard/applespi.c:306: warning: Function parameter or member 'capsl_command' not described in 'message'
 drivers/input/keyboard/applespi.c:306: warning: Function parameter or member 'bl_command' not described in 'message'
 drivers/input/keyboard/applespi.c:306: warning: Function parameter or member 'data' not described in 'message'

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201112110204.2083435-15-lee.jones@linaro.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>