Correct wave_mpmd setting in JGLOBAL_WAVE_INIT

- When the mpmd variable in the R&D env files was renamed to
mpmd_opt the wave_mpmd setting in JGLOBAL_WAVE_INIT was not
updated to match and thus broke the job when tested.
- Update the wave_mpmd setting in JGLOBAL_WAVE_INIT to use the
wave_mpmd setting defined in the env files instead of the old
mpmd variable.

Refs NOAA-EMC#1060

jobs/JGLOBAL_WAVE_INIT

@@ -64,7 +64,7 @@ fi
 
 # Set mpi serial command
 export wavempexec=${wavempexec:-"mpirun -n"}
-export wave_mpmd=${mpmd:-"cfp"}
+export wave_mpmd=${wave_mpmd:-"cfp"}
 
 # Execute the Script  
 $HOMEgfs/scripts/exgfs_wave_init.sh