drm/nouveau/nvif: Fix potential memory leak in nvif_vmm_ctor().

In the Linux kernel, the following vulnerability has been resolved: drm/nouveau/nvif: Fix potential memory leak in nvif_vmm_ctor(). When the nvif_vmm_type is invalid, we will return error directly without freeing the args in nvif_vmm_ctor(), which leading a memory leak. Fix it by setting the ret -EINVAL and goto done.