MAINTAINERS: Fix TTM tree

TTM uses drm-misc now.  Update the tree.

Cc: David Ward <david.ward@gatech.edu>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210503134736.1467003-1-alexander.deucher@amd.com

MAINTAINERS

@@ -6141,7 +6141,7 @@ M:	Christian Koenig <christian.koenig@amd.com>
 M:	Huang Rui <ray.huang@amd.com>
 L:	dri-devel@lists.freedesktop.org
 S:	Maintained
-T:	git git://people.freedesktop.org/~agd5f/linux
+T:	git git://anongit.freedesktop.org/drm/drm-misc
 F:	drivers/gpu/drm/ttm/
 F:	include/drm/ttm/