HID: wacom: Set input bits before registration

We shouldn't change the event flags of input devices after they get registered.
Otherwise, udev will not get notified of these flags and cannot setup the
devices properly.
This fixes the probing to set the input event flags on the input_mapped callback
instead of the probe function.

Reported-by: Bastien Nocera <hadess@hadess.net>
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Tested-by: Bastien Nocera <hadess@hadess.net>
Signed-off-by: Bastien Nocera <hadess@hadess.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>