clients: fix len-string formatting

clients: fix len-string formatting

All these have the printf format string wrong. "%*s" sets the field width but
does not limit the string to len bytes. You need to set precision instead to
limit to len bytes: "%.*s".

Found by grepping, after wondering why my WIP prints printed garbage at the
end.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>