nvmet-fc: update function documentation

Add minimum description of the hosthandle parameter for
nvmet_fc_rcv_ls_req() so that we can get rid of the following warning.

drivers/nvme//target/fc.c:2009: warning: Function parameter or member 'hosthandle' not described in 'nvmet_fc_rcv_ls_req

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>