Comment # 3 on bug 1225068 from Takashi Iwai

Likely the issue that has been fixed in the upstream already, commit
958cd6beab693f395ffe07814ef77d2b45e8b0fc
  Bluetooth: btusb: Fix the patch for MT7920 the affected to MT7921

I'm building a test kernel with the fix backport in OBS home:tiwai:bsc1225068
repo.  Once after the build finishes (takes an hour or so), it'll appear at
  http://download.opensuse.org/repositories/home:/tiwai:/bsc1225068/standard/

Could you give it a try later?

Note that it's an unofficial build, hence you'll need to disable Secure Boot if
it's on in BIOS.