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

 drivers/input/touchscreen/resistive-adc-touch.c:34: warning: cannot understand function prototype: 'struct grts_state '
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201104162427.2984742-10-lee.jones@linaro.orgSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>