mei: drop global me_client_index

Global me_client_index is used only during the enumeration process and
can be effectively replaced by me_addr data from the last enumeration
response as we always enumerate clients in the increasing order.

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