HID: wacom: do not attempt to switch mode while in probe

The Intuos Pro seems to not like when we set the features right after
being powered up. Instead of waiting during probe, we can schedule the
switch mode and LED control in a deferred worker so that we don't have the
5 secs of delay from USB when the device is not accessible.

The USB timeout delays were really a pain because if you happen to unplug
the tablet while it is still waiting, you are just adding 5 second timeouts
to the USB stack. Which means that a new plug of the same tablet will also
gets delayed, and will also attempt to access the hardware while in
.probe(). So the tablet doesn't appear in the dmesg, the user unplug/replug
it to make it appearing... and so on so forth.

Really, this is for the best :)

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: Jason Gerecke <jason.gerecke@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>