platform/x86: dell-laptop: don't register micmute LED if there is no token

On Dell G3-3590, error message is issued during boot up,
"platform::micmute: Setting an LED's brightness failed (-19)",
but there's no micmute led on the machine.

Get the related tokens of SMBIOS, GLOBAL_MIC_MUTE_DISABLE/ENABLE.
If one of two tokens doesn't exist,
don't call led_classdev_register() for platform::micmute.
After that, you wouldn't see the platform::micmute in /sys/class/leds/,
and the error message wouldn't see in dmesg.

Fixes: d00fa46e ("platform/x86: dell-laptop: Add micmute LED trigger support")
Signed-off-by: Koba Ko <koba.ko@canonical.com>
Reviewed-by: Mario Limonciello <Mario.limonciello@dell.com>
Reviewed-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/platform/x86/dell-laptop.c

@@ -2204,10 +2204,13 @@ static int __init dell_init(void)
 
 	dell_laptop_register_notifier(&dell_laptop_notifier);
 
-	micmute_led_cdev.brightness = ledtrig_audio_get(LED_AUDIO_MICMUTE);
-	ret = led_classdev_register(&platform_device->dev, &micmute_led_cdev);
-	if (ret < 0)
-		goto fail_led;
+	if (dell_smbios_find_token(GLOBAL_MIC_MUTE_DISABLE) &&
+	    dell_smbios_find_token(GLOBAL_MIC_MUTE_ENABLE)) {
+		micmute_led_cdev.brightness = ledtrig_audio_get(LED_AUDIO_MICMUTE);
+		ret = led_classdev_register(&platform_device->dev, &micmute_led_cdev);
+		if (ret < 0)
+			goto fail_led;
+	}
 
 	if (acpi_video_get_backlight_type() != acpi_backlight_vendor)
 		return 0;