Allow the adding of 'posval' for dynamic options like 'profile'

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/parse.h b/parse.h
index 8f7982a..9cda559 100644
--- a/parse.h
+++ b/parse.h
@@ -50,7 +50,7 @@
 	void *cb;			/* callback */
 	const char *help;		/* help text for option */
 	const char *def;		/* default setting */
-	const struct value_pair posval[PARSE_MAX_VP];/* possible values */
+	struct value_pair posval[PARSE_MAX_VP];/* possible values */
 	const char *parent;		/* parent option */
 	int (*verify)(struct fio_option *, void *);
 	const char *prof_name;		/* only valid for specific profile */