This patch converts the resource management in PCI nm256 driver with
devres as a clean up.  Each manual resource management is converted
with the corresponding devres helper, and the card object release is
managed now via card->private_free instead of a lowlevel snd_device.

This should give no user-visible functional changes.

Link: https://lore.kernel.org/r/20210715075941.23332-43-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>