drm/msm/hdmi: check return value after calling platform_get_resource_byname()

drm/msm/hdmi: check return value after calling platform_get_resource_byname()

It will cause null-ptr-deref if platform_get_resource_byname() returns NULL,
we need check the return value.

Fixes: c6a57a50ad56 ("drm/msm/hdmi: add hdmi hdcp support (V3)")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/482992/
Link: https://lore.kernel.org/r/20220422032227.2991553-1-yangyingliang@huawei.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>