usb: misc: sisusbvga: Avoid NULL pointer dereference from sisusb

A failed kzalloc() is reported with a dev_err that dereferences the null
sisusb, this will cause a NULL pointer deference error.

Instead, pass dev->dev to the dev_err() rather than &sisusb->sisusb_dev->dev

Smatch analysis:

drivers/usb/misc/sisusbvga/sisusb.c:3087 sisusb_probe() error: potential null
  dereference 'sisusb'.  (kzalloc returns null)
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/misc/sisusbvga/sisusb.c

@@ -3084,7 +3084,7 @@ static int sisusb_probe(struct usb_interface *intf,
 
 	/* Allocate memory for our private */
 	if (!(sisusb = kzalloc(sizeof(*sisusb), GFP_KERNEL))) {
-		dev_err(&sisusb->sisusb_dev->dev, "Failed to allocate memory for private data\n");
+		dev_err(&dev->dev, "Failed to allocate memory for private data\n");
 		return -ENOMEM;
 	}
 	kref_init(&sisusb->kref);