Increase wallclock limit for test

cime_config/testdefs/testlist_clm.xml

@@ -1974,7 +1974,7 @@
       <machine name="cheyenne" compiler="intel" category="aux_clm"/>
     </machines>
     <options>
-      <option name="wallclock">00:20:00</option>
+      <option name="wallclock">00:40:00</option>
       <option name="comment"  >Want one fates test on a large grid: Since FATES has cohorts, it has potential to be a massive memory consumer and netcdf array size maker, so the large grid test will help smoke out these types of issues (and it's a restart test to cover possible memory/netcdf size issues with the restart file).</option>
     </options>
   </test>