Required to allow sysupgrades from OpenWrt 19.07.
Closes#7071
Fixes: 98fbf2edc021 ("ath79: move TPLINK_HWID/_HWREV to parent for tplink-safeloader")
Tested-by: J. Burfeind <git@aiyionpri.me>
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
(cherry picked from commit 8ba71f1f6f2359f9cf54201e9fc037df33f123c0)