scsi: libfc: Supply some missing kerneldoc struct/function attributes/params

Fixes the following W=1 kernel build warning(s):

 drivers/scsi/libfc/fc_exch.c:66: warning: Function parameter or member 'left' not described in 'fc_exch_pool'
 drivers/scsi/libfc/fc_exch.c:66: warning: Function parameter or member 'right' not described in 'fc_exch_pool'
 drivers/scsi/libfc/fc_exch.c:100: warning: Function parameter or member 'lport' not described in 'fc_exch_mgr'
 drivers/scsi/libfc/fc_exch.c:727: warning: Function parameter or member 'ep' not described in 'fc_invoke_resp'
 drivers/scsi/libfc/fc_exch.c:727: warning: Function parameter or member 'sp' not described in 'fc_invoke_resp'
 drivers/scsi/libfc/fc_exch.c:727: warning: Function parameter or member 'fp' not described in 'fc_invoke_resp'

Link: https://lore.kernel.org/r/20200713074645.126138-2-lee.jones@linaro.org
Cc: Hannes Reinecke <hare@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>