Use Doxygen style comments consistently.

We were already using them for functions; use them for struct members
and enum values as well.

Change-Id: I89c1ef9e4a4f19424186b4da5855522bac0a2c4d
diff --git a/inc/vmapi/hf/call.h b/inc/vmapi/hf/call.h
index ac1ddff..102fd6c 100644
--- a/inc/vmapi/hf/call.h
+++ b/inc/vmapi/hf/call.h
@@ -31,7 +31,7 @@
 #define HF_MAILBOX_RECEIVE  0xff05
 #define HF_MAILBOX_CLEAR    0xff06
 
-/* The amount of data that can be sent to a mailbox. */
+/** The amount of data that can be sent to a mailbox. */
 #define HF_MAILBOX_SIZE 4096
 
 /* clang-format on */