tools/lib/lockdep: Fix link creation warning

This warning triggers if the .so library has already been linked:

 triton:~/tip/tools/lib/lockdep> make
  CC       common.o
  CC       lockdep.o
  CC       rbtree.o
  LD       liblockdep-in.o
  LD       liblockdep.a
  ln: failed to create symbolic link ‘liblockdep.so’: File exists
  LD       liblockdep.so.4.5.0-rc6

Overwrite the link.

Cc: Alfredo Alvarez Fernandez <alfredoalvarezfernandez@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>