emulators/visualboyadvance-m: unbreak with ffmpeg 4.0

src/common/ffmpeg.cpp:288:27: error: use of undeclared identifier 'FF_MIN_BUFFER_SIZE'

audio_buf = (u8 *)malloc(AUDIO_BUF_LEN);
                         ^

src/common/ffmpeg.cpp:88:36: note: expanded from macro 'AUDIO_BUF_LEN'

^

src/common/ffmpeg.cpp:288:27: error: use of undeclared identifier 'FF_MIN_BUFFER_SIZE'
src/common/ffmpeg.cpp:88:69: note: expanded from macro 'AUDIO_BUF_LEN'

^

src/common/ffmpeg.cpp:307:27: error: use of undeclared identifier 'FF_MIN_BUFFER_SIZE'

video_buf = (u8 *)malloc(VIDEO_BUF_LEN);
                         ^

src/common/ffmpeg.cpp:90:24: note: expanded from macro 'VIDEO_BUF_LEN'

^

src/common/ffmpeg.cpp:438:29: error: use of undeclared identifier 'AVFMT_RAWPICTURE'

if(oc->oformat->flags & AVFMT_RAWPICTURE) {
                        ^

src/common/ffmpeg.cpp:447:20: error: use of undeclared identifier 'FF_MIN_BUFFER_SIZE'

pkt.size = VIDEO_BUF_LEN;
           ^

src/common/ffmpeg.cpp:90:24: note: expanded from macro 'VIDEO_BUF_LEN'

^

src/common/ffmpeg.cpp:463:16: error: use of undeclared identifier 'FF_MIN_BUFFER_SIZE'

if(pkt.size > VIDEO_BUF_LEN) {
              ^

src/common/ffmpeg.cpp:90:24: note: expanded from macro 'VIDEO_BUF_LEN'

^

PR: 227726
Reported by: antoine (via exp-run)
Obtained from: upstream