nvme-fabrics: ignore invalid fast_io_fail_tmo values

Valid fast_io_fail_tmo values are integers >= 0 or -1 (disabled).
Prevent userspace from setting arbitrary negative values.

Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>