mei: amthif: allow the read completion after close

The amthif client connection is shared over multiple file descriptors.
In case a file descriptor was closed immediately after a write, the read
credits should be still available so the pending reads can be cleaned
from the queue, hence we cannot drop the control read list, this is
done only upon connection close.

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>