docs: dma-api: Fix description of the sync_sg API

Fix the description of the parameters to dma_sync_sg*. They should be the
same as the parameters to dma_map_sg(), not dma_map_single().

Signed-off-by: Brian Johannesmeyer <bjohannesmeyer@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20231103162120.3474026-1-bjohannesmeyer@gmail.com>