sound: Indent channel info lines for more readability

[christos]

Summary

Sponsored by: The FreeBSD Foundation
MFC after: 2 days

Test Plan

pcm0: <Realtek ALC257 (Analog 2.0+HP/2.0)> on hdaa0 (1p:2v/1r:1v) default
        snddev flags=0x2e2<AUTOVCHAN,BUSY,MPSAFE,REGISTERED,VPC>
        [pcm0:play:dsp0.p0]: spd 48000, fmt 0x00200010, flags 0x00002108, 0x00000004
            interrupts 155353, underruns 0, feed 155353, ready 0 [b:2048/1024/2|bs:2048/1024/2]
            channel flags=0x2108<TRIGGERED,BUSY,HAS_VCHAN>
            {userland} -> feeder_mixer(0x00200010) -> {hardware}
        pcm0:play:dsp0.p0[pcm0:virtual:dsp0.vp0]: spd 48000, fmt 0x00201000/0x00200010, flags 0x1000110c, 0x00000023, pid 8426 (firefox)
            interrupts 0, underruns 1318029, feed 1440797, ready 0 [b:0/0/0|bs:131072/65536/2]
            channel flags=0x1000110c<RUNNING,TRIGGERED,BUSY,HAS_SIZE,VIRTUAL>
            {userland} -> feeder_root(0x00201000) -> feeder_format(0x00201000 -> 0x00200010) -> feeder_volume(0x00200010) -> {hardware}
...

[zlei]

I'd recommend to add test plan to do a quick demonstration for the good effect of this change. Then it will help reviewing.