drm/amdgpu: 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 <[e-mail]>
Cc: Alex Deucher <[e-mail]>
Cc: "Christian König" <[e-mail]>
Cc: Xinhui Pan <[e-mail]>
Acked-by: Alex Deucher <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/amd/amdgpu/atombios_encoders.c

···
 	dig->bl_dev = bd;
 
 	bd->props.brightness = amdgpu_atombios_encoder_get_backlight_brightness(bd);
-	bd->props.power = FB_BLANK_UNBLANK;
+	bd->props.power = BACKLIGHT_POWER_ON;
 	backlight_update_status(bd);
 
 	DRM_INFO("amdgpu atom DIG backlight initialized\n");