vsh: mark ctl as unused in vshReadline

My commit removed the last use in the version for platforms
without readline.

Fixes: c937c1d2Signed-off-by: NJán Tomko <jtomko@redhat.com>

tools/vsh.c

@@ -3028,7 +3028,8 @@ vshReadlineDeinit(vshControl *ctl G_GNUC_UNUSED)
 }
 
 char *
-vshReadline(vshControl *ctl, const char *prompt)
+vshReadline(vshControl *ctl G_GNUC_UNUSED,
+            const char *prompt)
 {
     char line[1024];
     char *r;