Input: cyapa - fix misnaming of 'cyapa_i2c_write's 'reg' param

Input: cyapa - fix misnaming of 'cyapa_i2c_write's 'reg' param

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

 drivers/input/mouse/cyapa.c:130: warning: Function parameter or member 'reg' not described in 'cyapa_i2c_write'
 drivers/input/mouse/cyapa.c:130: warning: Excess function parameter 'ret' description in 'cyapa_i2c_write'

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Benson Leung <bleung@chromium.org>
Link: https://lore.kernel.org/r/20201104162427.2984742-3-lee.jones@linaro.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>