nvmet-fc: fix kernel-doc headers

This patch avoids that the kernel-doc tool complains about two function
headers when building with W=1.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>