locking/qspinlock: Fix 'wait_early' set but not used warning

When CONFIG_LOCK_EVENT_COUNTS is off, the wait_early variable will be
set but not used. This is expected. Recent compilers will not generate
wait_early code in this case.

Add the __maybe_unused attribute to wait_early for suppressing this
W=1 warning.
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20240222150540.79981-2-longman@redhat.com

Closes: https://lore.kernel.org/oe-kbuild-all/202312260422.f4pK3f9m-lkp@intel.com/

kernel/locking/qspinlock_paravirt.h

@@ -294,8 +294,8 @@ static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev)
 {
 	struct pv_node *pn = (struct pv_node *)node;
 	struct pv_node *pp = (struct pv_node *)prev;
+	bool __maybe_unused wait_early;
 	int loop;
-	bool wait_early;
 
 	for (;;) {
 		for (wait_early = false, loop = SPIN_THRESHOLD; loop; loop--) {