drm/nouveau/device: call nvkm_device_fini if nvkm_device_init fails

nvkm_device_fini is never called if a failure occurs in
nvkm_device_init, even when unloading the module. This can lead to a
resources leak (one example is the Tegra interrupt which would never be
freed in that case). Fix this by calling nvkm_device_fini in
nvkm_device_init's failure path.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>