staging: gasket: core: use bool type for ns_capable result

When gasket core was converted from using capable() to use ns_capable()
instead, the type of the variable holding the result should have been
converted from int to bool.

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