From: Heiner Kallweit <hkallweit1@gmail.com>
Date: Thu, 27 Jun 2019 23:19:09 +0200

DMA_API_HOWTO.txt includes an example explaining when
dma_sync_single_for_device() is not needed, and that example matches
our use case. The buffer isn't changed by the CPU and direction is
DMA_FROM_DEVICE, so we can remove the call to
dma_sync_single_for_device().

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>

Applied.