xfs: inode lockdep annotations broke non-lockdep build

Fix CONFIG_LOCKDEP=n build, because asserts I put in to ensure we
aren't overrunning lockdep subclasses in commit 0952c818 ("xfs:
clean up inode lockdep annotations") use a define that doesn't
exist when CONFIG_LOCKDEP=n

Only check the subclass limits when lockdep is actually enabled.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>