ui/input: Constify QemuInputHandler structure

Access to QemuInputHandlerState::handler are read-only.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Message-Id: <20231017131251.43708-1-philmd@linaro.org>
diff --git a/chardev/wctablet.c b/chardev/wctablet.c
index 43bdf6b..f4008bf 100644
--- a/chardev/wctablet.c
+++ b/chardev/wctablet.c
@@ -178,7 +178,7 @@
     }
 }
 
-static QemuInputHandler wctablet_handler = {
+static const QemuInputHandler wctablet_handler = {
     .name  = "QEMU Wacom Pen Tablet",
     .mask  = INPUT_EVENT_MASK_BTN | INPUT_EVENT_MASK_ABS,
     .event = wctablet_input_event,