staging: gasket: remove code for no physical device

gasket_enable_dev code for enabling a gasket device with no physical PCI
device registered shouldn't be necessary.

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