Surface runoff variable is mis-named in INITPOST_MPAS

[EricJames-NOAA]

We need to have surface runoff successfully passed through UPP for MPAS applications. The name is currently not correct.

[BenjaminBlake-NOAA]

@EricJames-NOAA I noticed this UPP issue is still open. Would you like to include this fix for the MPAS surface run-off variable with your PR #1520 or would you prefer to open a separate PR for this one? Thanks!