gnu date is present in our staging_dir which means squashfskit will fail
to build. Prevent also a race condition if coreutils is build after
squashfskit.

To prevent a race condition, depend on coreutils.

Acked-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Alexander Couzens <lynxis@fe80.eu>