nir/gcm: Fix a typo in a comment

Reported-by: Matt Turner <mattst88@gmail.com>
diff --git a/src/compiler/nir/nir_opt_gcm.c b/src/compiler/nir/nir_opt_gcm.c
index 9d7f59c..cff2315 100644
--- a/src/compiler/nir/nir_opt_gcm.c
+++ b/src/compiler/nir/nir_opt_gcm.c
@@ -320,7 +320,7 @@
    if (lca == NULL)
       return true;
 
-   /* We know have the LCA of all of the uses.  If our invariants hold,
+   /* We now have the LCA of all of the uses.  If our invariants hold,
     * this is dominated by the block that we chose when scheduling early.
     * We now walk up the dominance tree and pick the lowest block that is
     * as far outside loops as we can get.