msdkdec: fix msdkmjpegdec fail to decode.
MSDK defined common decoder parameter and mjpeg decoder parameter in same union. So if in case of mjpeg decode, we shouldn't set values to common decoder to avoid overlap the values to jpeg decoder.
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MSDK defined common decoder parameter and mjpeg decoder parameter in same union. So if in case of mjpeg decode, we shouldn't set values to common decoder to avoid overlap the values to jpeg decoder.