drm/bridge: panel: Fix device link for DRM_BRIDGE_ATTACH_NO_CONNECTOR

When external bridges are attached with DRM_BRIDGE_ATTACH_NO_CONNECTOR,
the panel bridge may also get the same flag, but in the .attach()
callback for the panel bridge a device link is added only when this
flag is not present; To make things worse, the .detach() callback
tries to delete the device link unconditionally and without checking
if it was created in the first place, crashing the kernel with a NULL
pointer kernel panic upon calling panel_bridge_detach().

Fix that by moving the device_link_add() call before checking if the
DRM_BRIDGE_ATTACH_NO_CONNECTOR flag is present.

Fixes: 199cf07e

 ("drm/bridge: panel: Add a device link between drm device and panel device")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Liu Ying <victor.liu@nxp.com>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230920082727.57729-1-angelogioacchino.delregno@collabora.com