qemu-char: convert vc backend to data-driven creation

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/ui/gtk.c b/ui/gtk.c
index 2947838..47b37e1 100644
--- a/ui/gtk.c
+++ b/ui/gtk.c
@@ -1591,7 +1591,7 @@
 static int nb_vcs;
 static CharDriverState *vcs[MAX_VCS];
 
-static CharDriverState *gd_vc_handler(ChardevVC *unused)
+static CharDriverState *gd_vc_handler(ChardevVC *unused, Error **errp)
 {
     CharDriverState *chr;