fpsync: Use printf instead of echo where necessary
fpsync: Use printf instead of echo where necessary

to avoid a potential clash between parameters and echo options.

This is a followup to 62c9287 (from GH PR #34).

See also: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/echo.html

martymac/fpart,martymac/fpart