nvmet-fc: fix missing check for no hostport struct

A hostport port pointer is allowed to be NULL as it is not allocated if
the lldd does not support the new interfaces for NVME LS request support.
The hostport free routine validates the handle but forgot to validate the
hostport pointer.

Validate the hostport pointer before using it to validate the handle.

Signed-off-by: James Smart <james.smart@broadcom.com>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>