Use the new MX_PROCESS_SIGNAL name

Change-Id: I08a640206ca9307ef7973c84a6d84f632b057025
diff --git a/benchmarks/spec_fixture.cc b/benchmarks/spec_fixture.cc
index cbc3db2..ffb9c02 100644
--- a/benchmarks/spec_fixture.cc
+++ b/benchmarks/spec_fixture.cc
@@ -228,7 +228,7 @@
     return handle;
   }
   status =
-      mx_handle_wait_one(handle, MX_SIGNAL_SIGNALED, MX_TIME_INFINITE, NULL);
+      mx_handle_wait_one(handle, MX_PROCESS_SIGNALED, MX_TIME_INFINITE, NULL);
 
   if (status != NO_ERROR) {
     LOG(ERROR) << "Failed to wait for process exiting " << args[0] << ":"