nvme-multipath: set ana_log_size to 0 after free ana_log_buf

Set ana_log_size to 0 when ana_log_buf is freed to make sure
nvme_mpath_init_identify will do the right thing when retrying
after an earlier failure.

Signed-off-by: Hou Tao <houtao1@huawei.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>