MAINTAINERS: soundwire: Add soundwire tree

Somehow the soundwire MAINTAINERS did not have the tree details, so add
it.

Signed-off-by: Vinod Koul <vkoul@kernel.org>
Link: https://lore.kernel.org/r/20210117071258.2541484-1-vkoul@kernel.org


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