hikey: fix uninitialized variable in ddr code

Fix uninitliazed variable in ddr driver code.
Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>

plat/hisilicon/hikey/hikey_ddr.c

@@ -385,7 +385,7 @@ static void ddrx_rdet(void)
 
 static void ddrx_wdet(void)
 {
-	unsigned int data, wdet, zero_bdl, dq[4];
+	unsigned int data, wdet, zero_bdl = 0, dq[4];
 	int i;
 
 	data = mmio_read_32((0xf712c000 + 0x0d0));