drm: zynqmp_dpsub: Fix an error handling path in zynqmp_dpsub_probe()

If zynqmp_dpsub_drm_init() fails, we must undo the previous
drm_bridge_add() call.

Fixes: be3f3042 ("drm: zynqmp_dpsub: Always register bridge")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Sean Anderson <sean.anderso@linux.dev>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/974d1b062d7c61ee6db00d16fa7c69aa1218ee02.1716198025.git.christophe.jaillet@wanadoo.fr