[SCSI] storvsc: NULL pointer dereference fix

If the initialization of storvsc fails, the storvsc_device_destroy()
causes NULL pointer dereference.

storvsc_bus_scan()
scsi_scan_target()
__scsi_scan_target()
scsi_probe_and_add_lun(hostdata=NULL)
scsi_alloc_sdev(hostdata=NULL)

sdev->hostdata = hostdata

now the host allocation fails

__scsi_remove_device(sdev)

calls sdev->host->hostt->slave_destroy() ==
storvsc_device_destroy(sdev)
access of sdev->hostdata->request_mempool

Signed-off-by: Ales Novak <[e-mail]>
Signed-off-by: Thomas Abraham <[e-mail]>
Reviewed-by: Jiri Kosina <[e-mail]>
Acked-by: K. Y. Srinivasan <[e-mail]>
Cc: [e-mail]
Signed-off-by: James Bottomley <[e-mail]>

drivers/scsi/storvsc_drv.c

···
 {
 	struct stor_mem_pools *memp = sdevice->hostdata;
 
+	if (!memp)
+		return;
+
 	mempool_destroy(memp->request_mempool);
 	kmem_cache_destroy(memp->request_pool);
 	kfree(memp);