Fix bugs in setting GxSpV_u and GxSpV_v in MOM_isopycnal_slopes#701

Hallberg-NOAA merged 2 commits into

NOAA-GFDL:dev/gfdlNOAA-GFDL/MOM6:dev/gfdlfrom

Wendazhang33:GxSpV_fixWendazhang33/MOM6-GFDL:GxSpV_fixCopy head branch name to clipboard