locking/Documentation: Update code path

lockdep code has been moved from kernel/ to kernel/locking/ by commit
8eddac3f103736163f49255bcb109edadea167f6 ("locking: Move the lockdep
code to kernel/locking/"). But, path to lockdep code in document was not
updated.

This commit updates the path.

Signed-off-by: SeongJae Park <sj38.park@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1421176921-27688-1-git-send-email-sj38.park@gmail.com
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-doc@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

Documentation/locking/lockdep-design.txt

@@ -34,7 +34,7 @@ The validator tracks lock-class usage history into 4n + 1 separate state bits:
 - 'ever held with STATE enabled'
 - 'ever held as readlock with STATE enabled'
 
-Where STATE can be either one of (kernel/lockdep_states.h)
+Where STATE can be either one of (kernel/locking/lockdep_states.h)
  - hardirq
  - softirq
  - reclaim_fs