ARM: zynq: Fix sparse warning in ddrc.c

Warning:
arch/arm/cpu/armv7/zynq/ddrc.c:43:24: warning: Using plain integer as NULL pointer

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/arch/arm/cpu/armv7/zynq/ddrc.c b/arch/arm/cpu/armv7/zynq/ddrc.c
index ba6a6ae..302654d 100644
--- a/arch/arm/cpu/armv7/zynq/ddrc.c
+++ b/arch/arm/cpu/armv7/zynq/ddrc.c
@@ -40,7 +40,7 @@
 		 * first stage bootloader. To get ECC to work all memory has
 		 * been initialized by writing any value.
 		 */
-		memset(0, 0, 1 * 1024 * 1024);
+		memset((void *)0, 0, 1 * 1024 * 1024);
 	} else {
 		puts("Memory: ECC disabled\n");
 	}