SCSI: Free resources when we return BLKPREP_INVALID

When called scsi_prep_fn return BLKPREP_INVALID, we should use the same
code with BLKPREP_KILL in scsi_prep_return.

Signed-off-by: Yiwen Jiang <jiangyiwen@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>