dmaengine: bcm2835-dma: Prevent suspend if DMA channel is busy

bcm2835-dma provides the service to others, so it should suspend
late and resume early. Suspend should be prevented in case a DMA
channel is still busy.

Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Link: https://lore.kernel.org/r/20241204165546.77941-1-wahrenst@gmx.net


Signed-off-by: Vinod Koul <vkoul@kernel.org>