Docs: FFmpeg plugin docs - ST30 PCM16 audio demuxer (#1174)

Fixes an error with -f parameter for receiving PCM16 audio via an FFmpeg
plugin (`-f mtl_st30p_pcm16` to `-f mtl_st30p`).

Author: MateuszGrabuszynski

ecosystem/ffmpeg_plugin/README.md

@@ -180,7 +180,7 @@ For pcm16 audio, use `mtl_st30p_pcm16` muxer, set `pcm_fmt` to `pcm16` for demux
 ```bash
 ffmpeg -stream_loop -1 -i test.wav -p_port 0000:af:01.1 -p_sip 192.168.96.3 -p_tx_ip 239.168.85.20 -udp_port 30000 -payload_type 97 -ptime 1ms -f mtl_st30p_pcm16 -
 
-ffmpeg -p_port 0000:af:01.0 -p_sip 192.168.96.2 -p_rx_ip 239.168.85.20 -udp_port 30000 -payload_type 97 -pcm_fmt pcm16 -ptime 1ms -channels 2 -f mtl_st30p_pcm16 -i "0" dump_pcm16.wav -y
+ffmpeg -p_port 0000:af:01.0 -p_sip 192.168.96.2 -p_rx_ip 239.168.85.20 -udp_port 30000 -payload_type 97 -pcm_fmt pcm16 -ptime 1ms -channels 2 -f mtl_st30p -i "0" dump_pcm16.wav -y
 ```
 
 ## 5. St20 GPU direct guide