fix typo in example for TRIM function

Change-Id: Id1bb170188f62d8f7d335d0797f2ffe027d16efe
Reviewed-on: https://gerrit.libreoffice.org/6976
Reviewed-by: Andras Timar <andras.timar@collabora.com>
Tested-by: Andras Timar <andras.timar@collabora.com>