drm/amd: Don't fail on backlight = 0

Amgpu's backlight update status function was
returning 1 (an error value) when the backlight
property was 0.  This breaks users that assume
0 is a valid backlight value (which is a
correct assumption)

If the user passes in a backlight value of 0,
tell them everything is fine, then write a value of
1 to hardware.
Signed-off-by: David Francis <David.Francis@amd.com>
Bugzilla: https://bugs.freedesktop.org/108668
Fixes: 416615ea9578 ("drm/amd/display: set backlight level limit to 1")
Cc: Suresh.Guttula@amd.com
Cc: Harry.Wentland@amd.com
Cc: Samantham@posteo.net
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -1573,21 +1573,23 @@ static int amdgpu_dm_backlight_update_status(struct backlight_device *bd)
 {
 	struct amdgpu_display_manager *dm = bl_get_data(bd);
 
+	/* backlight_pwm_u16_16 parameter is in unsigned 32 bit, 16 bit integer
+	 * and 16 bit fractional, where 1.0 is max backlight value.
+	 * bd->props.brightness is 8 bit format and needs to be converted by
+	 * scaling via copy lower byte to upper byte of 16 bit value.
+	 */
+	uint32_t brightness = bd->props.brightness * 0x101;
+
 	/*
 	 * PWM interperts 0 as 100% rather than 0% because of HW
-	 * limitation for level 0.So limiting minimum brightness level
+	 * limitation for level 0.  So limiting minimum brightness level
 	 * to 1.
 	 */
 	if (bd->props.brightness < 1)
-		return 1;
+		brightness = 0x101;
 
-	/* backlight_pwm_u16_16 parameter is in unsigned 32 bit, 16 bit integer
-	 * and 16 bit fractional, where 1.0 is max backlight value.
-	 * bd->props.brightness is 8 bit format and needs to be converted by
-	 * scaling via copy lower byte to upper byte of 16 bit value.
-	 */
 	if (dc_link_set_backlight_level(dm->backlight_link,
-			(bd->props.brightness * 0x101), 0, 0))
+			brightness, 0, 0))
 		return 0;
 	else
 		return 1;