Fix typo and incorrect variable name in balance.c comment

src/sipnet/balance.c

@@ -18,8 +18,8 @@ void getMassTotals(double *carbon, double *nitrogen) {
   }
 
   if (ctx.nitrogenCycle) {
-    // Note: this is the one place where we ust plantWoodC by itself; it's the
-    // reason plantNSCWoodCDelta was created, so that we can ignore it here.
+    // Note: this is the one place where we use plantWoodC by itself; it's the
+    // reason plantWoodCStorageDelta was created, so that we can ignore it here.
     *nitrogen =
         envi.plantWoodC / params.woodCN + envi.plantLeafC / params.leafCN +
         envi.fineRootC / params.fineRootCN + envi.coarseRootC / params.woodCN +