scsi: fnic: Use scsi_host_busy_iter() to traverse commands

Use scsi_host_busy_iter() to traverse commands instead of hand-crafted
routines walking the command list.

Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Ming Lei <[email protected]>
Signed-off-by: Hannes Reinecke <[email protected]>
Signed-off-by: Martin K. Petersen <[email protected]>

Author: hreinecke