sound: Do not return an error from chn_notify() if the children list is empty

[christos]

Summary

An empty children list does not mean that there is an error.

Reported by: Florian Walpen <[e-mail]>
Sponsored by: The FreeBSD Foundation
MFC after: 1 week

[dev_submerge.ch]

I can confirm that this fixes the panic experienced with D47917, and I don't see anything else that could be affected by the change in return value. Thank you!

[christos]

In D48156#1098827, @dev_submerge.ch wrote:

I can confirm that this fixes the panic experienced with D47917, and I don't see anything else that could be affected by the change in return value. Thank you!

Thank you for proposing this. :-)