tools/lib/lockdep: Fix undefined symbol prandom_u32

tools/lib/lockdep: Fix undefined symbol prandom_u32

__lock_pin_lock() now calls prandom_u32() which is not defined in
liblockdep.  __lock_pin_lock() and its caller lock_pin_lock() are dead
code in liblockdep, but we still need to provide a definition of
prandom_u32() in case lazy binding is disabled.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: a.p.zijlstra@chello.nl
Fixes: e7904a28f533 ("locking/lockdep, sched/core: Implement a better ...")
Link: http://lkml.kernel.org/r/20170525130005.5947-2-alexander.levin@verizon.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>