lsm: fix default return value for vm_enough_memory

1 is the return value that implements a "no-op" hook, not 0.

Cc: stable@vger.kernel.org
Fixes: 98e828a0

 ("security: Refactor declaration of LSM hooks")
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>