nvme-multipath: set nr_zones for zoned namespaces

The bio based drivers only require the request_queue's nr_zones is set,
so set this field in the head if the namespace path is zoned.

Fixes: 240e6ee2

 ("nvme: support for zoned namespaces")
Reported-by: Minwoo Im <minwoo.im.dev@gmail.com>
Cc: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>