Revert "staging: gasket: page table: hold references to device and pci_dev"

gasket_free_dev() is called only from driver PCI probe and remove
function. It is guaranteed that that pci_dev structure is not going
anywhere during that time; there is no need to take this additional
reference.

This reverts commit dd9d1502.

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