cros_ec: Fix deadlock when EC is not responsive at probe

When the EC is not responsive at probe, we try to get basic information
(protocol to use) later on through cros_xfer_cmd() call.
This patch makes sure there is no deadlock when re-probing the EC by
replacing call to cros_xfer_cmd() with send_command() in the function
cros_ec_get_host_command_version_mask(). Also, this patch adds the
function header indicating it must be called protected.

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
Signed-off-by: Benson Leung <bleung@chromium.org>