Documentation: sunxi: Update A13 user manual dead link

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

Documentation/arm/sunxi/README

@@ -25,4 +25,4 @@ SunXi family
         + Datasheet
 	  http://dl.linux-sunxi.org/A13/A13%20Datasheet%20-%20v1.12%20%282012-03-29%29.pdf
         + User Manual
-	  http://dl.linux-sunxi.org/A13/A13%20User%20Manual%20-%20v1.2%20%282013-08-08%29.pdf
+          http://dl.linux-sunxi.org/A13/A13%20User%20Manual%20-%20v1.2%20%282013-01-08%29.pdf