md: disconnect device from personality before trying to remove it.

When the HOT_REMOVE_DISK ioctl is used to remove a device, we
call remove_and_add_spares() which will remove it from the personality
if possible.  This improves the chances that the removal will succeed.

When writing "remove" to dev-XX/state, we don't.  So that can fail more easily.

So add the remove_and_add_spares() into "remove" handling.
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

drivers/md/md.c

@@ -2595,6 +2595,8 @@ state_store(struct md_rdev *rdev, const char *buf, size_t len)
 		else
 			err = -EBUSY;
 	} else if (cmd_match(buf, "remove")) {
+		clear_bit(Blocked, &rdev->flags);
+		remove_and_add_spares(rdev->mddev, rdev);
 		if (rdev->raid_disk >= 0)
 			err = -EBUSY;
 		else {