Typically, you should not make changes to files and directories in 'matlabroot'/toolbox.
The basic way to fix this is to reinstall MATLAB. But If you can find the original copy of 'griddata.m', you can replace yours with that one. You can type
on the MATLAB command prompt to see where it should be located.
Generally it should be located here: 'matlabroot'\toolbox\matlab\sparfun\gmres.m
to update the search path and cache file.