nvme-multipath: don't call blk_mark_disk_dead in nvme_mpath_remove_disk

nvme_mpath_remove_disk is called after del_gendisk, at which point a
blk_mark_disk_dead call doesn't make any sense.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Keith Busch <kbusch@kernel.org>