Pull sound fixes from Takashi Iwai:
 "All fixes are small and for stable:

   - a PCM ioctl race fix

   - yet another USB-audio hardening for malicious descriptors

   - Realtek ALC257 codec support"

* tag 'sound-4.15-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound:
  ALSA: pcm: prevent UAF in snd_pcm_info
  ALSA: hda/realtek - New codec support for ALC257
  ALSA: usb-audio: Add check return value for usb_string()
  ALSA: usb-audio: Fix out-of-bound error
  ALSA: seq: Remove spurious WARN_ON() at timer check