dell-led: use dell_smbios_find_token() for finding mic DMI tokens

With the advent of dell_smbios_find_token(), dell-led does not need to
perform any DMI walking on its own, but it can rather ask dell-smbios to
look up the DMI tokens it needs for changing the state of the microphone
LED.

Signed-off-by: Michał Kępień <kernel@kempniu.pl>
Reviewed-by: Pali Rohár <pali.rohar@gmail.com>
Acked-by: Jacek Anaszewski <j.anaszewski@samsung.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>