scsi: NCR5380: Withhold disconnect privilege for REQUEST SENSE

This is mostly needed because an AztecMonster II target has been observed
disconnecting REQUEST SENSE commands and then failing to reselect properly.

Suggested-by: Michael Schmitz <schmitzmic@gmail.com>
Tested-by: Michael Schmitz <schmitzmic@gmail.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>