_starpu_mpi_receive_early_data: simplify locking

_starpu_mpi_tag_get_data_handle_from_tag does not actually pose problem with
the progress mutex.

mpi/src/mpi/starpu_mpi_mpi.c

@@ -1157,9 +1157,7 @@ static void _starpu_mpi_receive_early_data(struct _starpu_mpi_envelope *envelope
 	_starpu_mpi_early_data_add(early_data_handle);
 
 	starpu_data_handle_t data_handle;
-	STARPU_PTHREAD_MUTEX_UNLOCK(&progress_mutex);
 	data_handle = _starpu_mpi_tag_get_data_handle_from_tag(envelope->data_tag);
-	STARPU_PTHREAD_MUTEX_LOCK(&progress_mutex);
 
 	// TODO: rather select some memory node next to the NIC
 	unsigned buffer_node = STARPU_MAIN_RAM;