Also use 0.125nldas2 grid for rof

Since the rof grid is identical to lnd, we should be able to use idmap
for the rof <-> lnd mappings.

config/cesm/config_grids.xml

@@ -122,11 +122,11 @@
 
     <!-- Regional NLDAS-2 grid over the U.S. (0.125 degree resolution;
          25-53N, 235-293E), with mask from NLDAS-2 atmospheric drivers -->
-    <model_grid alias="nldas2_mnldas2" compset="DATM.+CLM">
+    <model_grid alias="nldas2_rnldas2_mnldas2" compset="DATM.+CLM">
       <grid name="atm">0.125nldas2</grid>
       <grid name="lnd">0.125nldas2</grid>
       <grid name="ocnice">0.125nldas2</grid>
-      <grid name="rof">null</grid>
+      <grid name="rof">0.125nldas2</grid>
       <mask>nldas2</mask>
     </model_grid>
 
@@ -1103,6 +1103,7 @@
       <desc>5x5 Amazon regional case -- only valid for DATM/CLM compset</desc>
     </domain>
 
+    <!-- This grid is also used by ROF -->
     <domain name="0.125nldas2">
       <nx>464</nx> <ny>224</ny>
       <file grid="atm|lnd" mask="nldas2">$DIN_LOC_ROOT/share/domains/domain.clm/domain.lnd.0.125nldas2_0.125nldas2.190410.nc</file>