drm/panel: novatek-nt35950: fix return value check in nt35950_probe()

mipi_dsi_device_register_full() never returns NULL pointer, it
will return ERR_PTR() when it fails, so replace the check with
IS_ERR().

Fixes: 623a3531 ("drm/panel: Add driver for Novatek NT35950 DSI DriverIC panels")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20241029123957.1588-1-yangyingliang@huaweicloud.com


Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20241029123957.1588-1-yangyingliang@huaweicloud.com