Update diffusion parameters yaml (#1200)

This PR updates the diffusion parameter path in the yaml so that it
matches workflow changes. I separate global workflow PR will be issued
shortly.

parm/aero/berror/aero_diffusionparm.yaml.j2

@@ -40,11 +40,11 @@ background error:
       - horizontal:
           fixed value: {{ horiz_len }} 
         write:
-          filepath: "{{ DATA }}/berror/diffusion_hz" 
+          filepath: "{{ DATA }}/diffusion/diffusion_hz" 
       - vertical:
           levels: {{ npz_ges }} 
           fixed value: {{ fixed_val }} 
           as gaussian: true
         write:
-          filepath: "{{ DATA }}/berror/diffusion_hz" 
+          filepath: "{{ DATA }}/diffusion/diffusion_vt"