MAINTAINERS: Add sun4i-drm git repo

Add the git tree where the sun4i-drm patches are hosted.
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>

MAINTAINERS

@@ -4175,6 +4175,7 @@ L:	dri-devel@lists.freedesktop.org
 S:	Supported
 F:	drivers/gpu/drm/sun4i/
 F:	Documentation/devicetree/bindings/display/sunxi/sun4i-drm.txt
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/mripard/linux.git
 
 DRM DRIVERS FOR AMLOGIC SOCS
 M:	Neil Armstrong <narmstrong@baylibre.com>