dma-mapping: fix DMA API tracing for chained scatterlists

scatterlist allocations can be chained, and thus all iterations need to
use the chain-aware iterators.  Switch the newly added tracing to use the
proper iterators so that they work with chained scatterlists.

Fixes: 038eb433 ("dma-mapping: add tracing for dma-mapping API calls")
Reported-by:  <syzbot+95e4ef83a3024384ec7a@syzkaller.appspotmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sean Anderson <sean.anderson@linux.dev>
Tested-by:  <syzbot+95e4ef83a3024384ec7a@syzkaller.appspotmail.com>