[COMPMID-1593] CLPad failing

Change-Id: Id1604fbf3b8fc98d5b45fa8266dd8182cf0ce204
Reviewed-on: https://eu-gerrit-1.euhpc.arm.com/149137
Reviewed-by: Georgios Pinitas <georgios.pinitas@arm.com>
Tested-by: bsgcomp <bsgcomp@arm.com>
diff --git a/arm_compute/core/PixelValue.h b/arm_compute/core/PixelValue.h
index ce3726b..31705bd 100644
--- a/arm_compute/core/PixelValue.h
+++ b/arm_compute/core/PixelValue.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, 2017 ARM Limited.
+ * Copyright (c) 2016-2018 ARM Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -36,7 +36,7 @@
 public:
     /** Default constructor: value initialized to 0 */
     PixelValue()
-        : value{ { 0 } }
+        : value{ { uint64_t(0) } }
     {
     }
     /** Initialize the union with a U8 pixel value