scsi: NCR5380: Don't clear busy flag when abort fails

When NCR5380_abort() returns FAILED, the driver forgets that the target is
still busy. Hence, further commands may be sent to the target, which may fail
during selection and produce the error message, "reselection after won
arbitration?". Prevent this by leaving the busy flag set when NCR5380_abort()
fails.

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>