dell-led: use dell_smbios_send_request() for performing SMBIOS calls

Instead of using the WMI wrapper, dell-led can take advantage of
dell_smbios_send_request() for performing the SMBIOS calls required to
change 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>