acer-wmi: Update MAINTAINERS

I don't have the time or much interest these days in maintaining acer-wmi, as I
don't have access to newer Acer hardware. As he's been doing most of the work
these days anyway, Joey Lee has kindly agreed to take over.

Signed-off-by: Carlos Corbacho <carlos@strangeworlds.co.uk>
Cc: Joey Lee <jlee@novell.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>