sound: Fix snd_pcm_readv()/writev() to use iov access functions

sound: Fix snd_pcm_readv()/writev() to use iov access functions

Fix snd_pcm_readv()/writev() to use iov access functions rather than poking
at the iov_iter internals directly.

Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20230925120309.1731676-4-dhowells@redhat.com
Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
cc: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
cc: Jens Axboe <axboe@kernel.dk>
cc: Suren Baghdasaryan <surenb@google.com>
cc: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
cc: alsa-devel@alsa-project.org
Signed-off-by: Christian Brauner <brauner@kernel.org>