rtldsa_get_mib_desc() is always well defined and only looks into
the configuration structure. Drop it and use direct data assignment
where needed. While we are here drop all NULL checks because
mib_desc is never unset.
Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Link: https://github.com/openwrt/openwrt/pull/22219
Signed-off-by: Robert Marko <robimarko@gmail.com>