omap: SDMA: Fix omap_stop_dma() API for channel linking

OMAP sDMA driver API omap_stop_dma() doesn't really stop the dma when used
in linking scenario.

The DMA channel needs to be disabled before resetting the chain.
Also fix clearing of the OMAP_DMA_ACTIVE status in the linked case.

Cc: Hari n <hari.zoom@gmail.com>
Cc: Jarkko Nikula <jhnikula@gmail.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Venkatraman S <svenkatr@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>