drm/nouveau/kms/nv50: hide unused variables

After a recent change, two variables are only used in an #ifdef:

drivers/gpu/drm/nouveau/dispnv50/disp.c: In function 'nv50_sor_atomic_disable':
drivers/gpu/drm/nouveau/dispnv50/disp.c:1569:13: error: unused variable 'ret' [-Werror=unused-variable]
 1569 |         int ret;
      |             ^~~
drivers/gpu/drm/nouveau/dispnv50/disp.c:1568:28: error: unused variable 'aux' [-Werror=unused-variable]
 1568 |         struct drm_dp_aux *aux = &nv_connector->aux;
      |                            ^~~

Move them into the same conditional block, along with the nv_connector variable
that becomes unused during that fix.

Fixes: 75703380 ("drm/nouveau/kms/nv50-: fixup sink D3 before tearing down link")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Danilo Krummrich <dakr@redhat.com>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230925155930.677620-1-arnd@kernel.org