sunxi: dram_sun4i/5i: use DRAM_MEMORY_TYPE_DDR3 instead of magic number 3

Since DRAM_MEMORY_TYPE_DDR3 is defined let's use it instead of magic
number 3.

Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/board/sunxi/dram_sun5i_auto.c b/board/sunxi/dram_sun5i_auto.c
index a5f4f8b..517506c 100644
--- a/board/sunxi/dram_sun5i_auto.c
+++ b/board/sunxi/dram_sun5i_auto.c
@@ -7,7 +7,7 @@
 static struct dram_para dram_para = {
 	.clock = CONFIG_DRAM_CLK,
 	.mbus_clock = CONFIG_DRAM_MBUS_CLK,
-	.type = 3,
+	.type = DRAM_MEMORY_TYPE_DDR3,
 	.rank_num = 1,
 	.density = 0,
 	.io_width = 0,