mei: fix max number of open handles

There was internal confusion in wether bus message
clinet (0) is counted in or not

The bitmap me_clients_map that accomodate
was initialized w/o it (255) but later on it
the clinet 0 was reserved

Thus were able to open only 252 instead of 253 clients

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