mei: kill usless struct mei_io_list

kill useless mei_io_list list wrapper and use directly
struct mei_cl_cb mei_cb which was its only member for managing io queues

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>