HID: wacom: Assign boolean values to a bool variable

Fix the following coccicheck warnings:

./drivers/hid/wacom_wac.c:2536:2-6: WARNING: Assignment of
0/1 to bool variable.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Zhong <abaci-bugfix@linux.alibaba.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>