mei: amthif: clean command queue upon disconnection

In order to prevent memory leak clean up the amthif command
queue upon disconnection. The issue may happen only on error path
as the command queue is cleaned upon file descriptor close.
And remove the cleanup from mei_cl_flush_queues as this code
is never reached for amthif client.

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