dmaengine: imx-sdma: remove duplicated sdma_load_context

Since sdma_transfer_init() will do sdma_load_context before any
sdma transfer, no need once more in sdma_config_channel().

Signed-off-by: Robin Gong <yibin.gong@nxp.com>
Acked-by: Vinod Koul <vkoul@kernel.org>