staging: gasket: gasket page table functions use bool return type

Convert from int to bool return type for gasket page table functions
that return values used as booleans.

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