f2fs: project ids aren't idmapped

Project ids are only settable filesystem wide in the initial namespace.
They don't take the mount's idmapping into account.

Note, that after we converted everything over to struct mnt_idmap
mistakes such as the one here aren't possible anymore as struct
mnt_idmap cannot be passed to functions that operate on k{g,u}ids.

Acked-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>