HID: lenovo: Add checks to fix of_led_classdev_register

In lenovo_probe_tpkbd(), the function of_led_classdev_register() could
return an error value that is unchecked. The fix adds these checks.

Signed-off-by: Aditya Pakki <pakki001@umn.edu>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>