greybus: properly annotate struct gb_control_timesync_enable_request

A patch from created struct gb_control_timesync_enable_request,
but forgot to properly annotate that the fields are little-endian.  The
code is correct in treating them this way, so there isn't a bug, but
sparse complains.

Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>