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: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>