MAINTAINERS: Add file patterns for dma device tree bindings

Submitters of device tree binding documentation may forget to CC
the subsystem maintainer if this is missing.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Vinod Koul <vinod.koul@intel.com>
Cc: dmaengine@vger.kernel.org
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

MAINTAINERS

@@ -3773,6 +3773,7 @@ Q:	https://patchwork.kernel.org/project/linux-dmaengine/list/
 S:	Maintained
 F:	drivers/dma/
 F:	include/linux/dmaengine.h
+F:	Documentation/devicetree/bindings/dma/
 F:	Documentation/dmaengine/
 T:	git git://git.infradead.org/users/vkoul/slave-dma.git