cmdutils_opencl: Use av_malloc_array()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/hevc: Use av_malloc(z)_array()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avfilter/f_ebur128: Use av_malloc_array()

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