Update MPD-21 to 21.22

Changelog ver 0.21.22 (2020/04/02)

• database
  • simple: optimize startup
• input
  • curl: fix streaming errors on Android
• playlist
  • rss: support MIME type application/xml
• mixer
  • android: new mixer plugin for "sles" output
• Android
  • TV support
• Windows
  • fix time zone offset check
• fix build failures with uClibc-ng