This patch converts the resource management in serial u16550 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/20210715075941.23332-76-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>