fix typo in example for TRIM function

Change-Id: I4f543e290652e160e02e75e7e178a8647bc91f50
Reviewed-on: https://gerrit.libreoffice.org/6977
Reviewed-by: Andras Timar <andras.timar@collabora.com>
Tested-by: Andras Timar <andras.timar@collabora.com>