media: mtk-mdp: Fix error handling in probe function

In the Linux kernel, the following vulnerability has been resolved: media: mtk-mdp: Fix error handling in probe function Add mtk_mdp_unregister_m2m_device() on the error handling path to prevent resource leak. Add check for the return value of vpu_get_plat_device() to prevent null pointer dereference. And vpu_get_plat_device() increases the reference count of the returned platform device. Add platform_device_put() to prevent reference leak.