dell-smbios: make da_tokens static

As dell-laptop has been changed to use dell_smbios_find_token() instead
of directly accessing members of the da_tokens table, the latter can be
marked static.

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>