qemu -enable-sound sometimes aborts with a message saying
        oss: write audio
        system error: Unknown error 572
	(the actual error number changes)
For some reason that I haven't understood yet, write() to the dsp device
failes sometimes and qemu aborts on the first failure. It seems to be safe
to ignore these failures and keep going instead.

The problem first occured to me with an OS/2 guest. I have had a report
that it also happened in Windows.

The attached patch fixes this.