snd channel: fix accessing freed memory
snd channel: fix accessing freed memory

snd_channel_put freed "channel", and then channel->worker was accessed.
It caused segmentation faults during connections and disconnections of the client.

ya-mouse/spice,ya-mouse/spice,alon/spice-server,elmarco/spice,mathslinux/spice,Fantu/spice,alon/spice-server,fgouget/spice,freedesktop-unofficial-mirror/spice__spice,mathslinux/spice,fgouget/spice,ya-mouse/spice,elmarco/spice,SPICE/spice,elmarco/spice,mathslinux/spice,mathslinux/spice,elmarco/spice,Fantu/spice,freedesktop-unofficial-mirror/spice__spice,alon/spice-server,freedesktop-unofficial-mirror/spice__spice,fgouget/spice,alon/spice-server,mathslinux/spice,elmarco/spice,fgouget/spice,Fantu/spice,freedesktop-unofficial-mirror/spice__spice,alon/spice-server,Fantu/spice,freedesktop-unofficial-mirror/spice__spice,SPICE/spice,SPICE/spice