Fix process_stage comment in pipeline_template

Use consistently E_{} notation to denote the computation done at a given
stage instead of a mix of Stage_{} and E_{}.

pipepar/pipeline_template.c

@@ -30,7 +30,7 @@ struct timespec stage_time;
 data_t result = 0;
 
 
-/* $Stage_{i+1} (data_{j+1}) = E_i (data_{j+1}) + E_{i+1} (data_j)$ */
+/* $E_{i+1} (data_{j+1}) = E_i (data_{j+1}) + E_{i+1} (data_j)$ */
 void process_stage(data_t *prev_pipeline_stage, data_t *next_pipeline_stage)
 {
 	long i;