Commit 2910ff17
introduced a regression which would remove a recently added spare via
slot_store. Revert part of the patch which touches slot_store() and add
the disk directly using pers->hot_add_disk()

Fixes: 2910ff17 ("md: remove_and_add_spares() to activate specific
rdev")
Signed-off-by: NGoldwyn Rodrigues <rgoldwyn@suse.com>
Signed-off-by: NPawel Baldysiak <pawel.baldysiak@intel.com>
Signed-off-by: NNeilBrown <neilb@suse.com>