drm/nouveau/disp: fix use-after-free in error handling of nouveau_connector_create

In the Linux kernel, the following vulnerability has been resolved:

drm/nouveau/disp: fix use-after-free in error handling of nouveau_connector_create

We can't simply free the connector after calling drm_connector_init on it. We need to clean up the drm side first.

It might not fix all regressions from commit 2b5d1c29f6c4 ("drm/nouveau/disp: PIOR DP uses GPIO for HPD, not PMGR AUX interrupts"), but at least it fixes a memory corruption in error handling related to that commit.