ASoC: dmaengine: Convert to generic PCM copy ops

This patch converts the ASoC dmaenging driver code to use the new
unified PCM copy callback.  It's a straightforward conversion from
*_user() to *_iter() variants.

The process callback is still using the direct pointer as of now, but
it'll be converted in the next patch.

Note that copy_from/to_iter() returns the copied bytes, hence the
error condition is adjusted accordingly.

Reviewed-by: Mark Brown <broonie@kernel.org>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Link: https://lore.kernel.org/r/20230815190136.8987-22-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>