rocr: unitialized size variable caused huge memory/space allocation (#1232)

Signed-off-by: Alex Xie <AlexBin.Xie@amd.com>

projects/rocr-runtime/runtime/hsa-runtime/core/util/simple_heap.h

@@ -134,7 +134,7 @@ template <typename Allocator> class SimpleHeap {
     // Find best fit.
     auto free_fragment = free_list_.lower_bound(bytes);
     uintptr_t base;
-    size_t size;
+    size_t size = 0;
 
     if (free_fragment != free_list_.end()) {
       base = free_fragment->second;