When bumping to 4.19 the patch responsible for scaning flash for FIS
partition got left out. Without it devices with RedBoot bootloader using
automatic partitions detection in dts won't boot with the new kernel.
Fixes: 3771176 ("ath79: add support for linux 4.19")
Signed-off-by: Tomasz Maciej Nowak <tomek_n@o2.pl>
