Fix usb sound card for behringer-umc22.conf
I have a usb sound card 08bb:2902 Texas Instruments PCM2902 Audio Codec
:
drq@opi4:~$ lsusb
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 002: ID 08bb:2902 Texas Instruments PCM2902 Audio Codec
Because it only has one channel, so this fixed it.