ALSA: fireface: fix return value in error path of isochronous resources reservation

Even if isochronous resources reservation fails, error code doesn't return
in pcm.hw_params callback.

Cc: <[e-mail]> #5.3+
Fixes: 55162d2bb0e8 ("ALSA: fireface: reserve/release isochronous resources in pcm.hw_params/hw_free callbacks")
Signed-off-by: Takashi Sakamoto <[e-mail]>
Link: https://lore.kernel.org/r/20191209151655.GA8090@workstation
Signed-off-by: Takashi Iwai <[e-mail]>

sound/firewire/fireface/ff-pcm.c

···
 		mutex_unlock(&ff->mutex);
 	}
 
-	return 0;
+	return err;
 }
 
 static int pcm_hw_free(struct snd_pcm_substream *substream)