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>

MAINTAINERS

@@ -16654,6 +16654,7 @@ R:	Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
 R:	Sanyog Kale <sanyog.r.kale@intel.com>
 L:	alsa-devel@alsa-project.org (moderated for non-subscribers)
 S:	Supported
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/vkoul/soundwire.git
 F:	Documentation/driver-api/soundwire/
 F:	drivers/soundwire/
 F:	include/linux/soundwire/