mei: amthif: use mei_cl_alloc_cb for allocating cbs

Use mei_cl_alloc_cb wrapper instead of open code steps

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>