staging: gasket: gasket_get_device drop check for NULL pci_dev

The pci_dev field of a struct gasket_dev can never be NULL, there's no
need to check for this in gasket_get_device().

Reported-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Todd Poynor <toddpoynor@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>