ALSA: virmidi: Allocate resources with device-managed APIs

This patch converts the card object management with devres as a clean
up.  The remove callback gets reduced by that.

This should give no user-visible functional changes.

Link: https://lore.kernel.org/r/20210715075941.23332-74-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>