dm: uclass: fix comment copy/paste error

The uclass_next_device() routine continues a previously started device
iteration. Change the description that is copied from
uclass_first_device().

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/include/dm/uclass.h b/include/dm/uclass.h
index 1bc62d5..484d166 100644
--- a/include/dm/uclass.h
+++ b/include/dm/uclass.h
@@ -297,7 +297,7 @@
  *
  * The device returned is probed if necessary, and ready for use
  *
- * This function is useful to start iterating through a list of devices which
+ * This function is useful to iterate through a list of devices which
  * are functioning correctly and can be probed.
  *
  * @devp: On entry, pointer to device to lookup. On exit, returns pointer