When CONFIG_POSTPROC is set there was a now
invalid reference to cm->filter_level.

Changed to cpi->mb.e_mbd.lf.filter_level in line with
change Iaf5fb71c33719cdfa1b991f671caf071be9ea035

Change-Id: If746e60044903f7ba8d0d346225b3d015226c7d0