COMPMID-2819: Fix const interface of IMemoryRegion.

Signed-off-by: Georgios Pinitas <georgios.pinitas@arm.com>
Change-Id: Ib241c1b7b35645f5702de874004eced806883cd5
Reviewed-on: https://review.mlplatform.org/c/2609
Reviewed-by: Manuel Bottini <manuel.bottini@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Giuseppe Rossini <giuseppe.rossini@arm.com>
Tested-by: Arm Jenkins <bsgcomp@arm.com>
diff --git a/src/runtime/GLES_COMPUTE/GCMemoryRegion.cpp b/src/runtime/GLES_COMPUTE/GCMemoryRegion.cpp
index 45fd6e8..2ffd9f2 100644
--- a/src/runtime/GLES_COMPUTE/GCMemoryRegion.cpp
+++ b/src/runtime/GLES_COMPUTE/GCMemoryRegion.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018 ARM Limited.
+ * Copyright (c) 2018-2020 ARM Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -42,7 +42,7 @@
     return _mapping;
 }
 
-void *IGCMemoryRegion::buffer() const
+const void *IGCMemoryRegion::buffer() const
 {
     return _mapping;
 }