mjpeg: support mpo

Fixes stereoscopic_photo.mpo

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 1d23e5246c)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/rawdec.c

@@ -252,7 +252,7 @@ AVInputFormat ff_gsm_demuxer = {
 #endif
 
 #if CONFIG_MJPEG_DEMUXER
-FF_DEF_RAWVIDEO_DEMUXER(mjpeg, "raw MJPEG video", NULL, "mjpg,mjpeg", CODEC_ID_MJPEG)
+FF_DEF_RAWVIDEO_DEMUXER(mjpeg, "raw MJPEG video", NULL, "mjpg,mjpeg,mpo", CODEC_ID_MJPEG)
 #endif
 
 #if CONFIG_MLP_DEMUXER