build: slightly change files to pass compilation

Compiled using Clang and encountered errors on ambiguous pointer
type, implicit conversion NULL to bool, and unused function, etc.
As a fix, this patch slightly updates the related codes.

Change-Id: I4a73d66293313dda36749036f5c73aaf2a445231

test/ctrl/test_hsa.cpp

@@ -62,7 +62,7 @@ bool TestHsa::Initialize(int /*arg_cnt*/, char** /*arg_list*/) {
     if (!hsa_rsrc_->GetGpuAgentInfo(agent_id, &agent_info_)) {
       agent_info_ = NULL;
       std::cerr << "> error: agent[" << agent_id << "] is not found" << std::endl;
-      return NULL;
+      return false;
     }
   }
   std::clog << "> Using agent[" << agent_info_->dev_index << "] : " << agent_info_->name << std::endl;