HID: elo: Revert USB reference counting

Commit 817b8b9c ("HID: elo: fix memory leak in elo_probe") introduced
memory leak on error path, but more importantly the whole USB reference
counting is not needed at all in the first place, as the driver itself
doesn't change the reference counting in any way, and the associated
usb_device is guaranteed to be kept around by USB core as long as the
driver binding exists.

Reported-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: fbf42729 ("HID: elo: update the reference count of the usb device structure")
Fixes: 817b8b9c ("HID: elo: fix memory leak in elo_probe")
Signed-off-by: Jiri Kosina <jkosina@suse.cz>