dm: Tidy up some header file comments

Fix up the style of a few comments and add/clarify a few others.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/dm/device.h b/include/dm/device.h
index 6005e7e..9077490 100644
--- a/include/dm/device.h
+++ b/include/dm/device.h
@@ -124,7 +124,7 @@
  * This is typically only useful for device-tree-aware drivers (those with
  * an of_match), since drivers which use platdata will have the data
  * provided in the U_BOOT_DEVICE() instantiation.
- * ops: Driver-specific operations. This is typically a list of function
+ * @ops: Driver-specific operations. This is typically a list of function
  * pointers defined by the driver, to implement driver functions required by
  * the uclass.
  * @flags: driver flags - see DM_FLAGS_...