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>