[SCSI] fix OOPS due to clearing eh_action prior to aborting eh command

The eh_action semaphore in scsi_eh_send_command is cleared after a
command timeout.  The command is subsequently aborted and the abort
will try to call scsi_done() on it.  Unfortunately, the scsi_eh_done()
routine unconditinally completes the semaphore (which is now null).
Fix this race by makiong the scsi_eh_done() routine check that the
semaphore is non null before completing it (mirroring the ordinary
command done/timeout logic).
Signed-off-by: NJames Bottomley <James.Bottomley@SteelEye.com>

drivers/scsi/scsi_error.c

@@ -422,10 +422,15 @@ static int scsi_eh_completed_normally(struct scsi_cmnd *scmd)
  **/
 static void scsi_eh_done(struct scsi_cmnd *scmd)
 {
+	struct completion     *eh_action;
+
 	SCSI_LOG_ERROR_RECOVERY(3,
 		printk("%s scmd: %p result: %x\n",
 			__FUNCTION__, scmd, scmd->result));
-	complete(scmd->device->host->eh_action);
+
+	eh_action = scmd->device->host->eh_action;
+	if (eh_action)
+		complete(eh_action);
 }
 
 /**