lavc/mjpegdec: avoid printing useless message in default log level

The change of bps from 0 doesn't contain any info useful to the
user. This message is now at info log level only if the original
value is !=0, otherwise pushed back to debug log level. The
original value is displayed additionally.
Signed-off-by: Moritz Barsnick <barsnick@gmx.net>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/mjpegdec.c

@@ -282,7 +282,7 @@ int ff_mjpeg_decode_sof(MJpegDecodeContext *s)
     }
 
     if (s->avctx->bits_per_raw_sample != bits) {
-        av_log(s->avctx, AV_LOG_INFO, "Changing bps to %d\n", bits);
+        av_log(s->avctx, s->avctx->bits_per_raw_sample > 0 ? AV_LOG_INFO : AV_LOG_DEBUG, "Changing bps from %d to %d\n", s->avctx->bits_per_raw_sample, bits);
         s->avctx->bits_per_raw_sample = bits;
         init_idct(s->avctx);
     }