mesa/st: Free st_translate with FREE macro.

To match CALLOC_STRUCT macro.

Fixes memory corruption on Windows when u_memory's memory debugging is
enabled.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>

src/mesa/state_tracker/st_glsl_to_tgsi.cpp

@@ -5365,7 +5365,7 @@ out:
          debug_printf("%s: translate error flag set\n", __func__);
       }
 
-      free(t);
+      FREE(t);
    }
 
    return ret;