HID: wacom: Check for string overflow from strscpy calls

The strscpy function is able to return an error code when a copy would
overflow the size of the destination. The copy is stopped and the buffer
terminated before overflow actually occurs so it is safe to continue
execution, but we should still produce a warning should this occur.

Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Reviewed-by: Ping Cheng <ping.cheng@wacom.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>