staging: gasket: convert gasket_mmap_has_permissions to bool return

gasket_mmap_has_permissions() should return a boolean value.

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