drm/nouveau/disp: Revert a NULL check inside nouveau_connector_get_modes

drm/nouveau/disp: Revert a NULL check inside nouveau_connector_get_modes

The original commit adding that check tried to protect the kenrel against
a potential invalid NULL pointer access.

However we call nouveau_connector_detect_depth once without a native_mode
set on purpose for non LVDS connectors and this broke DP support in a few
cases.

Cc: Olaf Skibbe <news@kravcenko.com>
Cc: Lyude Paul <lyude@redhat.com>
Closes: https://gitlab.freedesktop.org/drm/nouveau/-/issues/238
Closes: https://gitlab.freedesktop.org/drm/nouveau/-/issues/245
Fixes: 20a2ce87fbaf8 ("drm/nouveau/dp: check for NULL nv_connector->native_mode")
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230805101813.2603989-1-kherbst@redhat.com