fix no opcode mapping warnings:
warn:sc:32739:14:sc/source/filter/oox/formulabase.cxx:1431: OpCodeProviderImpl::initFuncOpCode - no opcode mapping for function ODF 'ORG.LIBREOFFICE.FORECAST.ETS.MULT' <-> OOXML '_xlfn.FORECAST.ETS.MULT'
'ORG.LIBREOFFICE.FORECAST.ETS.PI.MULT'
'ORG.LIBREOFFICE.FORECAST.ETS.STAT.MULT'

Change-Id: I55bbf79b40944d76486085f5aceb842197c51b5c
Reviewed-on: https://gerrit.libreoffice.org/22914Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>