drm/panel: panel-novatak-nt35510: Use backlight power constants

Replace FB_BLANK_ constants with their counterparts from the
backlight subsystem. The values are identical, so there's no
change in functionality or semantics.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Neil Armstrong <neil.armstrong@linaro.org>
Cc: Jessica Zhang <quic_jesszhan@quicinc.com>
Reviewed-by: Jessica Zhang <quic_jesszhan@quicinc.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240731122311.1143153-4-tzimmermann@suse.de

drivers/gpu/drm/panel/panel-novatek-nt35510.c

@@ -1166,7 +1166,7 @@ static int nt35510_probe(struct mipi_dsi_device *dsi)
 			bl->props.brightness = nt->conf->wrdisbv;
 		else
 			bl->props.brightness = 255;
-		bl->props.power = FB_BLANK_POWERDOWN;
+		bl->props.power = BACKLIGHT_POWER_OFF;
 		nt->panel.backlight = bl;
 	}