video: exynos_dp: Fix bug when checking dp->irq

Fix a bug where we check !dp->irq instead of the correct check for
-ENXIO.

Signed-off-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Olof Johansson <olofj@chromium.org>
Signed-off-by: Jingoo Han <jg1.han@samsung.com>