drm/panel-novatek-nt35510: Emit an error message if power off fails

Returning an error code from a mipi_dsi remove callback fails, this is
silently ignored. (mipi_dsi_drv_remove() propagates the return value to
device_remove() which ignores it.) So emit an error code in the driver
remove function and return 0.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220708094922.1408248-3-u.kleine-koenig@pengutronix.de