chardev: force write all when recording replay logs

chardev: force write all when recording replay logs

This is mostly a problem within avocado as serial generally isn't busy
enough to overfill pipes. However the consequences of recording a
failed write will haunt us on replay when the log will be out of sync
to the playback.

Fixes: https://gitlab.com/qemu-project/qemu/-/issues/2010
Acked-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20231211091346.14616-13-alex.bennee@linaro.org>