avdevice/lavfi: Use av_malloc_array()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avfilter/af_aphaser: Use av_malloc_array()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avfilter/af_channelmap: Use av_mallocz_array()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avfilter/af_amix: Use av_mallocz_array()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>