audiod: Don't init slot info unless opening the receiver succeeds.

audiod: Don't init slot info unless opening the receiver succeeds.

Currently we set the slot's audio format number even if the receiver could not
be opened. This confuses the slot clearing code as no writer is active in
this case which triggers the assertion

	para_audiod: audiod.c:384: close_writers: Assertion `s->wns'

Fix it by not touching the slot info structure unless we have successfully started
the receiver. Also perform some minor cleanups while we're at it.

Thanks to Gerrit Renker for pointing out this bug.