acer-wmi: build depends on i8042

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Carlos Corbacho <carlos@strangeworlds.co.uk>
Signed-off-by: Len Brown <len.brown@intel.com>