HID: wacom: Fix wacom_probe error handling

OLEDs/LED are not critical for tablet functioning thus ignore OLED/LED
initialisation failures.

This patch does clean up all the sysfs attribute files in error paths.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Tested-by: Przemo Firszt <przemo@firszt.eu>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>