r8169: remove not needed call to dma_sync_single_for_device

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>
Signed-off-by: David S. Miller <davem@davemloft.net>