backlight: 88pm860x_bl: fix checkpatch warning

This patch fixes the checkpatch warning as below:

  WARNING: quoted string split across lines
Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/video/backlight/88pm860x_bl.c

@@ -117,8 +117,8 @@ static int pm860x_backlight_set(struct backlight_device *bl, int brightness)
 	data->current_brightness = value;
 	return 0;
 out:
-	dev_dbg(chip->dev, "set brightness %d failure with return "
-		"value:%d\n", value, ret);
+	dev_dbg(chip->dev, "set brightness %d failure with return value: %d\n",
+		value, ret);
 	return ret;
 }