[SCSI] Fix protection scsi_data_buffer leak

We would leak a scsi_data_buffer if the free_list command was of the
protected variety.

Reported-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Stable Tree <stable@kernel.org>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>