Input: turbografx - clear unused function pointers

tgfx_parport_cb is a local uninitialized structure and the member
function pointers will be pointing to arbitrary locations unless they
are cleared.

Fixes: 4de27a638a99 ("Input: turbografx - use parallel port device model")
Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/joystick/turbografx.c

@@ -181,6 +181,7 @@ static void tgfx_attach(struct parport *pp)
 	n_buttons = tgfx_cfg[port_idx].args + 1;
 	n_devs = tgfx_cfg[port_idx].nargs - 1;
 
+	memset(&tgfx_parport_cb, 0, sizeof(tgfx_parport_cb));
 	tgfx_parport_cb.flags = PARPORT_FLAG_EXCL;
 
 	pd = parport_register_dev_model(pp, "turbografx", &tgfx_parport_cb,