liblockdep: Fix undefined symbol prandom_u32

liblockdep: 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.

Fixes: e7904a28f533 ("locking/lockdep, sched/core: Implement a better ...")
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Gbp-Pq: Topic bugfix/all
Gbp-Pq: Name liblockdep-fix-undefined-symbol-prandom_u32.patch