ofp-actions: Fix memory leak.

Coverity CID 279274 reports leaking previously allocated
'error' buffer when 'return xasprintf("input too big");'.

Cc: Usman Ansari <uansari@vmware.com>
Signed-off-by: William Tu <u9012063@gmail.com>
Reviewed-by: Greg Rose <gvrose8192@gmail.com>

lib/ofp-actions.c

@@ -6657,6 +6657,7 @@ parse_CT(char *arg, const struct ofpact_parse_params *pp)
     }
 
     if (ofpbuf_oversized(pp->ofpacts)) {
+        free(error);
         return xasprintf("input too big");
     }