Calling nand_do_upgrade() from platform_pre_upgrade() was obsoleted in the commit30f61a34b4("base-files: always use staged sysupgrade"). This change brings bcm53xx in sync with other targets and allows dropping backward compatibility code. It shouldn't change any user visible behavior. Signed-off-by: Rafał Miłecki <rafal@milecki.pl> (cherry picked from commitccf8a8e863)