Correction for MaxCPUsPerNode logic

This is a correction to commit 308b7432

src/plugins/select/cons_res/job_test.c

@@ -290,7 +290,7 @@ static uint16_t _allocate_sc(struct job_record *job_ptr, bitstr_t *core_map,
 		}
 		free_cpu_count += free_cores[i] * threads_per_core;
 		if (used_cpu_array[i])
-			used_cpu_count = used_cores[i] * threads_per_core;
+			used_cpu_count += used_cores[i] * threads_per_core;
 	}
 	xfree(used_cores);
 	xfree(used_cpu_array);