dm: core: Correct the return value for uclass_find_first_device()

This function returns -ENODEV when there is no device. This is
inconsistent with other functions, such as uclass_find_next_device(),
which returns 0.

Update it and tidy up the incorrect '-1' values in the comments.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/include/dm/uclass-internal.h b/include/dm/uclass-internal.h
index 6977995..6e3f15c 100644
--- a/include/dm/uclass-internal.h
+++ b/include/dm/uclass-internal.h
@@ -69,7 +69,7 @@
  * The device is not prepared for use - this is an internal function.
  * The function uclass_get_device_tail() can be used to probe the device.
  *
- * @return 0 if OK (found or not found), -1 on error
+ * @return 0 if OK (found or not found), -ve on error
  */
 int uclass_find_first_device(enum uclass_id id, struct udevice **devp);
 
@@ -81,7 +81,7 @@
  * The device is not prepared for use - this is an internal function.
  * The function uclass_get_device_tail() can be used to probe the device.
  *
- * @return 0 if OK (found or not found), -1 on error
+ * @return 0 if OK (found or not found), -ve on error
  */
 int uclass_find_next_device(struct udevice **devp);