Fix UB bug in extensions/cl_khr_command_buffer/command_buffer_event_s…

…ync.cpp

RunCombufWaitForSecQueueCombuf() is launching two clEnqueueFillBuffer commands
on two separate queues, however both had the same buffer argument, and there
was no synchronization between the commands.

* add an event dependency to the second FillBuffer to ensure correct execution
* change the fill pattern of the first FillBuffer to a different pattern

test_conformance/extensions/cl_khr_command_buffer/command_buffer_event_sync.cpp

@@ -583,7 +583,7 @@ struct CommandBufferEventSync : public BasicCommandBufferTest
 
         // process secondary queue
         error =
-            clEnqueueFillBuffer(queue_sec, in_mem, &pattern_pri, sizeof(cl_int),
+            clEnqueueFillBuffer(queue_sec, in_mem, &pattern_sec, sizeof(cl_int),
                                 0, data_size(), 0, nullptr, nullptr);
         test_error(error, "clEnqueueFillBuffer failed");
 
@@ -594,7 +594,7 @@ struct CommandBufferEventSync : public BasicCommandBufferTest
 
         // process primary queue
         error = clEnqueueFillBuffer(queue, in_mem, &pattern_pri, sizeof(cl_int),
-                                    0, data_size(), 0, nullptr, event_ptrs[0]);
+                                    0, data_size(), 1, &test_event, event_ptrs[0]);
         test_error(error, "clEnqueueFillBuffer failed");
 
         cl_event wait_list[] = { test_event,