Move 480-mtd-set-rootfs-to-be-root-dev.patch to hack-5.10 and fix assumption
about the block device index.
Fixes: 2809d00007 ("kernel: support FIT partition parser on mtdblock devices")
Acked-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>