drm/bridge/sii8620: add missing error handling in probe

devm_request_threaded_irq result should be checked for errors.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1487764057-23362-1-git-send-email-a.hajda@samsung.com