spi: rockchip-sfc: Remove redundant IO operations

Coherent dma buffer is uncached and memcpy is enough.

Signed-off-by: Jon Lin <jon.lin@rock-chips.com>
Link: https://lore.kernel.org/r/20210821124925.6066-1-jon.lin@rock-chips.com


Signed-off-by: Mark Brown <broonie@kernel.org>