acl_profiler: Add assert to check for nullptr for accel_def

acl_find_accel_def ensures that the returned value is not NULL.

Author: haoxian2

src/acl_profiler.cpp

@@ -614,6 +614,7 @@ CL_API_ENTRY cl_int CL_API_CALL clGetProfileDataDeviceIntelFPGA(
                                            "autorun kernel profiling enabled";
       ERR_RET(status, program->context, message);
     }
+    assert(accel_def != NULL);
 
     // use autodiscovery info to find out how many words will be read from the
     // profiler