doxygen: use correct comment syntax

This issue was caused by uncrustify not correctly converting the doxygen
comments.

Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Change-Id: Ie6dc3b057a08603b670cb27312e5f0d989426e6c
Reviewed-on: http://openocd.zylin.com/431
Tested-by: jenkins

src/helper/command.c

@@ -291,7 +291,7 @@ static struct command **command_list_for_parent(
 
 static void command_free(struct command *c)
 {
-	/* / @todo if command has a handler, unregister its jim command! */
+	/** @todo if command has a handler, unregister its jim command! */
 
 	while (NULL != c->children) {
 		struct command *tmp = c->children;