mdadm/r5cache: allow adding journal to array without journal

Currently, --add-journal can be only used to recreate broken journal
for arrays with journal since  creation. As the kernel code getting
more mature, this constraint is no longer necessary.

This patch allows --add-journal to add journal to array without
journal.

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Jes Sorensen <jsorensen@fb.com>
2 files changed