avfilter: fix plane validity checks

Fixes out of array accesses

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
static av_cold void uninit(AVFilterContext *ctx)
{
    KerndeintContext *kerndeint = ctx->priv;

    av_free(kerndeint->tmp_data[0]);
}

static av_cold void uninit(AVFilterContext *ctx)
{
    KerndeintContext *kerndeint = ctx->priv;

    av_free(kerndeint->tmp_data[0]);
}
