drm: bridge: it66121: fix an error code in it66121_probe()

This code is passing the wrong variable to PTR_ERR() so it doesn't
return the correct error code.

Fixes: 988156dc ("drm: bridge: add it66121 driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/YJ+ZX3BdKPAN0pUZ@mwanda