MAINTAINERS: switch dmaengine tree to kernel.org

I have switched DMAengine tree to kernel.org now, so update in
MAINTAINERS file

Signed-off-by: Vinod Koul <vkoul@kernel.org>
Link: https://lore.kernel.org/r/20200623143729.781403-1-vkoul@kernel.org


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