drm/mediatek: Fix platform_get_irq() error checking

drm/mediatek: Fix platform_get_irq() error checking

The platform_get_irq() function returns negative error codes on failure
and positive non-zero IRQ numbers on success.  It never returns NULL. Fix
the error checking to look for negatives, and change "hdmi->irq" from
unsigned int to just int.

Fixes: 8d0f79886273 ("drm/mediatek: Introduce HDMI/DDC v2 for MT8195/MT8188")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
https://patchwork.kernel.org/project/dri-devel/patch/aSW0p5sqnJVJsqDO@stanley.mountain/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>