COMPMID-2980 (Nightly) armv7a build failures

Change-Id: I8c2a20fc345694d1ad6e0fe63e4f22fb73e6c1df
Signed-off-by: Michalis Spyrou <michalis.spyrou@arm.com>
Signed-off-by: Michele Di Giorgio <michele.digiorgio@arm.com>
Reviewed-on: https://review.mlplatform.org/c/2463
Tested-by: Arm Jenkins <bsgcomp@arm.com>
diff --git a/arm_compute/core/PixelValue.h b/arm_compute/core/PixelValue.h
index 8c2ab92..52b1f65 100644
--- a/arm_compute/core/PixelValue.h
+++ b/arm_compute/core/PixelValue.h
@@ -103,6 +103,15 @@
                 break;
         }
     }
+    /** Initialize the union with a S8 pixel value
+     *
+     * @param[in] v S8 value.
+     */
+    PixelValue(int8_t v)
+        : PixelValue()
+    {
+        value.s8 = v;
+    }
     /** Initialize the union with a U8 pixel value
      *
      * @param[in] v U8 value.