MAINTAINERS: add Documentation files to dmaengine entry

We were missing the Documentation files in the entry so add it now. While at
it also remove comment on slave-dma for the tree

Signed-off-by: Vinod Koul <vinod.koul@intel.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index fd3771c..b3f5493 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3080,7 +3080,8 @@
 S:	Maintained
 F:	drivers/dma/
 F:	include/linux/dma*
-T:	git git://git.infradead.org/users/vkoul/slave-dma.git (slave-dma)
+F:	Documentation/dmaengine/
+T:	git git://git.infradead.org/users/vkoul/slave-dma.git
 
 DME1737 HARDWARE MONITOR DRIVER
 M:	Juerg Haefliger <juergh@gmail.com>