ath10k: DMA related fixes for high latency devices

Several DMA related functions (such as the dma_map_xxx functions)
are not used with high latency devices and don't need to be invoked
in this case.

Signed-off-by: Erik Stromdahl <erik.stromdahl@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>