Input: wacom - cleanup a return value for the old Bamboo

The old code may call input_sync() without sending any other events.
While it will be suppressed by the input core not calling it at all
is still cheaper.

Signed-off-by: Ping Cheng <pingc@wacom.com>
Reviewed-by: Chris Bagwell <chris@cnpbagwell.com>
Reviewed-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>