[SCSI] libsas: prevent double completion of scmds from eh

We invoke task->task_done() to free the task in the eh case, but at this
point we are prepared for scsi_eh_flush_done_q() to finish off the scmd.

Introduce sas_end_task() to capture the final response status from the
lldd and free the task.

Also take the opportunity to kill this warning.
drivers/scsi/libsas/sas_scsi_host.c: In function ‘sas_end_task’:
drivers/scsi/libsas/sas_scsi_host.c:102:3: warning: case value ‘2’ not in enumerated type ‘enum exec_status’ [-Wswitch]

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
diff --git a/include/scsi/libsas.h b/include/scsi/libsas.h
index 10eb2ea..071041b 100644
--- a/include/scsi/libsas.h
+++ b/include/scsi/libsas.h
@@ -452,7 +452,10 @@
 };
 
 enum exec_status {
-	/* The SAM_STAT_.. codes fit in the lower 6 bits */
+	/* The SAM_STAT_.. codes fit in the lower 6 bits, alias some of
+	 * them here to silence 'case value not in enumerated type' warnings
+	 */
+	__SAM_STAT_CHECK_CONDITION = SAM_STAT_CHECK_CONDITION,
 
 	SAS_DEV_NO_RESPONSE = 0x80,
 	SAS_DATA_UNDERRUN,