dell-smbios: don't return an SMBIOS buffer from dell_smbios_send_request()

An SMBIOS buffer pointer does not need to be returned by
dell_smbios_send_request(), because SMBIOS call results are stored in
the buffer exported by the module.

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