drm/mediatek: Do not check for 0 return after calling platform_get_irq()

It is not possible for platform_get_irq() to return 0. Use the
return value from platform_get_irq().

Signed-off-by: Ruan Jinjie <ruanjinjie@huawei.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20230803040401.3067484-3-ruanjinjie@huawei.com/


Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>