ALSA: core: Warn on empty module

The module argument passed to snd_card_new() must be a valid non-NULL
pointer when the module support is enabled.  Since ASoC driver passes
the argument from each snd_soc_card definition, one may forget to set
the owner field and lead to a NULL module easily.

For catching such an overlook, add a WARN_ON() in snd_card_new().
Also, put the card->module assignment in the ifdef block for a very
minor optimization.

Link: https://lore.kernel.org/r/20200624160300.21703-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/init.c

@@ -203,7 +203,10 @@ int snd_card_new(struct device *parent, int idx, const char *xid,
 	mutex_unlock(&snd_card_mutex);
 	card->dev = parent;
 	card->number = idx;
+#ifdef MODULE
+	WARN_ON(!module);
 	card->module = module;
+#endif
 	INIT_LIST_HEAD(&card->devices);
 	init_rwsem(&card->controls_rwsem);
 	rwlock_init(&card->ctl_files_rwlock);