Avoid defining snow_prepobs_path twice

Author: jiaruidong2017

parm/snow/jcb-base.yaml.j2

@@ -84,7 +84,7 @@ snow_obsdatain_path: "{{DATA}}/obs"
 snow_obsdatain_prefix: "{{OPREFIX}}"
 snow_obsdatain_suffix: ".tm00.bufr_d"
 snow_obsdataout_path: "{{DATA}}/diags"
-snow_prepobs_path: "{{DATA}}/prep"
+snow_prepobs_path: "{{ snow_prepobs_path }}"
 snow_obsdataout_prefix: diag_
 snow_obsdataout_suffix: "_{{ current_cycle | to_YMDH }}.nc"
 ims_scf_obs_suffix: "{{ ims_scf_obs_suffix }}"