Fix buffer overrun of postproc_state.limits

Fix buffer overrun of postproc_state.limits

Always allocate cpi->common.postproc_state.limits using unscaled width.

With ./configure --enable-pic --enable-decode-perf-tests
--enable-encode-perf-tests --enable-encode-perf-tests
--enable-vp9-highbitdepth --enable-better-hw-compatibility
--enable-internal-stats --enable-postproc --enable-vp9-postproc
--enable-error-concealment --enable-coefficient-range-checking
--enable-postproc-visualizer --enable-multi-res-encodin
--enable-vp9-temporal-denoising --enable-webm-io --enable-libyuv
segfaults tend to occur in VP9/DatarateOnePassCbrSvcSingleBR.* tests.

This is an analogue to issue
https://bugs.chromium.org/p/webm/issues/detail?id=1374
where a buffer allocated using a scaled width is reused after scaling
back to the original size. Unfortunately, in this case the unscaled
width doesn't appear to be known in the immediated context of the
allocation, so the the signature of vp9_post_proc_frame needs to be
changed to provide that information in order to provide a similar fix
as in #1374.

Signed-off-by: Matthias Räncker <theonetruecamper@gmx.de>
Change-Id: I6f943aafbb3484ee94c5b38d7fcdd9d53fce3e5f