Input: touchscreen - use sysfs_emit[_at]() instead of scnprintf()

Follow the advice of the Documentation/filesystems/sysfs.rst and show()
should only use sysfs_emit() or sysfs_emit_at() when formatting the
value to be returned to user space.

Signed-off-by: ye xingchen <ye.xingchen@zte.com.cn>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Oliver Graute <oliver.graute@kococonnector.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>