examples: Pass --sync=0 to htrun

By default, htrun uses the Greentea protocol which involves sync
packets. But when comparing a plain application with a log, no
synchronization is involved and htrun should not send sync packets or
expect any response from the device. So --sync=0 should be used.

Note: If an application runs fast enough and matches the log before
synchronization times out (when --sync is not set to 0), htrun treats
it as a pass. But this is not reliable especially when TF-M (which
takes time to boot) is used.

Signed-off-by: Lingkai Dong <lingkai.dong@arm.com>