scsi: Change scsi_scan() to be able to return value

scsi: Change scsi_scan() to be able to return value

With DM_SCSI this function will return more than one return value to
cover errors.

Suggested-by: Simon Glass <[email protected]>
Signed-off-by: Michal Simek <[email protected]>
Reviewed-by: Tom Rini <[email protected]>
Reviewed-by: Simon Glass <[email protected]>