nvme-fc: Fix wrong return value in __nvme_fc_init_request()

On an error exit path, a negative error code should be returned
instead of a positive return value.

Fixes: e399441d

 ("nvme-fabrics: Add host support for FC transport")
Cc: James Smart <jsmart2021@gmail.com>
Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>