lockdep: Move lockdep_assert_locked() under #ifdef CONFIG_PROVE_LOCKING

When lockdep_assert_locked() is unused, it prevents kernel builds
with clang, `make W=1` and CONFIG_WERROR=y, CONFIG_LOCKDEP=y and
CONFIG_PROVE_LOCKING=n:

  kernel/locking/lockdep.c:160:20: error: unused function 'lockdep_assert_locked' [-Werror,-Wunused-function]

Fix this by moving it under the respective ifdeffery.

See also commit 6863f56 ("kbuild: allow Clang to find unused static
inline functions for W=1 build").

[Boqun: add more config information of the error]

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20241202193445.769567-1-andriy.shevchenko@linux.intel.com

Author: andy-shev

kernel/locking/lockdep.c

@@ -157,10 +157,12 @@ static inline void lockdep_unlock(void)
 	__this_cpu_dec(lockdep_recursion);
 }
 
+#ifdef CONFIG_PROVE_LOCKING
 static inline bool lockdep_assert_locked(void)
 {
 	return DEBUG_LOCKS_WARN_ON(__owner != current);
 }
+#endif
 
 static struct task_struct *lockdep_selftest_task_struct;