mpegvideo_enc: Don't call ff_h263dsp_init unconditionally

This fixes builds with e.g. --disable-decoders --disable-encoders
--enable-encoder=mjpeg.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/mpegvideo_enc.c

@@ -708,7 +708,8 @@ av_cold int ff_MPV_encode_init(AVCodecContext *avctx)
                           2 * 64 * sizeof(uint16_t), fail);
     }
 
-    ff_h263dsp_init(&s->h263dsp);
+    if (CONFIG_H263_ENCODER)
+        ff_h263dsp_init(&s->h263dsp);
     if (!s->dct_quantize)
         s->dct_quantize = ff_dct_quantize_c;
     if (!s->denoise_dct)