qdev: fix a typo in comment

Found by reading code.

Signed-off-by: Li Qiang <liq3ea@gmail.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index 36b788a..046d8f1 100644
--- a/hw/core/qdev.c
+++ b/hw/core/qdev.c
@@ -643,7 +643,7 @@
  * the string depends on the property type.  Legacy properties are only
  * needed for "info qtree".
  *
- * Do not use this is new code!  QOM Properties added through this interface
+ * Do not use this in new code!  QOM Properties added through this interface
  * will be given names in the "legacy" namespace.
  */
 static void qdev_property_add_legacy(DeviceState *dev, Property *prop,