mei: prepare read cb for fixed address clients on the receive path only.

The read callbacks for the fixed address clients, that don't have flow
control are built now on the receive path. In order to have a single
allocation place we remove the allocation from the read request.

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>