HID: wacom: convert sysfs sprintf/snprintf family to sysfs_emit

Fix the following coccicheck warning:

./drivers/hid/wacom_sys.c:1828:8-16: WARNING: use scnprintf or sprintf.

Reported-by: Abaci <Robot&lt;abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>