v4l: xilinx: scd: Don't mark channel as disabled in .s_stream(0)

v4l: xilinx: scd: Don't mark channel as disabled in .s_stream(0)

Commit 2e77607047c6 ("xilinx: v4l2: dma: Add multiple output support")
incorrectly calls .s_stream(0) on all channels when one of them gets
disabled, causing all the other channels to hang. Work around this by
not disabling the channel in .s_stream(0). The channel will be disabled
in xscd_dma_terminate_all() which should be safe as long as
dmaengine_terminate_all() is called after xvip_pipeline_set_stream().

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Hyun Kwon <hyun.kwon@xilinx.com>