Fix gang item wait on dependency signals

Gang items have to wait on dependency signals as well as the leader.
Copies should not start if shaders are still operating on memory
to be copied.

Change-Id: I99703b420045ebcba2c9da39ec64678129dc140f

runtime/hsa-runtime/core/runtime/amd_gpu_agent.cpp

@@ -963,10 +963,9 @@ hsa_status_t GpuAgent::DmaCopy(void* dst, core::Agent& dst_agent,
     hsa_status_t stat;
     size_t chunk = std::min(remainder_size, (size + gang_factor - 1)/gang_factor);
     if (!blit->GangLeader() && !gang_signals.empty()) {
-      std::vector<core::Signal*> dep_signals_null(0); // only leader has to wait on dependencies
       stat = blit->SubmitLinearCopyCommand(reinterpret_cast<uint8_t*>(dst) + offset,
                                            reinterpret_cast<const uint8_t*>(src) + offset,
-                                           chunk, dep_signals_null,
+                                           chunk, dep_signals,
                                            *gang_signals[gang_sig_count], gang_signals);
       gang_sig_count++;
     } else {