fdo#76409: Write output cell string to <text:p> element when saving to ods.

The change was made by accident.

Change-Id: Ife2461b0fca6e3ea5a65d72d985d1e0976737b5a
(cherry picked from commit a0752fa4246dc71b64907c679657a1af3cb617e1)
Reviewed-on: https://gerrit.libreoffice.org/9014
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>