mei: amthif: drop mei_amthif_send_cmd

Incorporate the mei_amthif_send_cmd code into its only caller:
mei_amthif_run_next_cmd

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>