fixed GARI equation

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@57967 15284696-431f-4ddb-bdfa-cd5b030d7da7

imagery/i.vi/gari.c

@@ -7,7 +7,7 @@ double ga_ri(double redchan,double nirchan,double bluechan,double greenchan)
 {
     double result;
     {
-        result = (nirchan - (greenchan - (bluechan - redchan)))/(nirchan - (greenchan - (bluechan + redchan)));
+        result = (nirchan - (greenchan - (bluechan - redchan)))/(nirchan - (greenchan + (bluechan - redchan)));
     }
     return result;
 }