libvpxenc: only set noise reduction w/vp8

this quiets a warning:
Failed to set VP8E_SET_NOISE_SENSITIVITY codec control: Unspecified
internal error

Reviewed-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: James Zern <jzern@google.com>

libavcodec/libvpxenc.c

@@ -525,9 +525,10 @@ static av_cold int vpx_init(AVCodecContext *avctx,
         codecctl_int(avctx, VP8E_SET_ARNR_STRENGTH,    ctx->arnr_strength);
     if (ctx->arnr_type >= 0)
         codecctl_int(avctx, VP8E_SET_ARNR_TYPE,        ctx->arnr_type);
-    codecctl_int(avctx, VP8E_SET_NOISE_SENSITIVITY, avctx->noise_reduction);
-    if (avctx->codec_id == AV_CODEC_ID_VP8)
+    if (avctx->codec_id == AV_CODEC_ID_VP8) {
+        codecctl_int(avctx, VP8E_SET_NOISE_SENSITIVITY, avctx->noise_reduction);
         codecctl_int(avctx, VP8E_SET_TOKEN_PARTITIONS,  av_log2(avctx->slices));
+    }
 #if FF_API_MPV_OPT
     FF_DISABLE_DEPRECATION_WARNINGS
     if (avctx->mb_threshold) {