ALSA: isa: Avoid passing NULL to memory allocators

We used to pass NULL to memory allocators for ISA devices due to
historical reasons.  But we prefer rather a proper device object to be
assigned, so let's fix it by replacing snd_dma_isa_data() call with
card->dev reference, and kill snd_dma_isa_data() definition.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>