dmaengine: imx-sdma: correct sdmac->status in sdma_handle_channel_loop()

sdma_handle_channel_loop() is the handler of cyclic tx.  One period
success does not really mean the success of the tx.  Instead of
DMA_SUCCESS, DMA_IN_PROGRESS should be the one to tell.

Signed-off-by: Shawn Guo <shawn.guo@freescale.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>