Both is_rwsem_reader_owned() and rwsem_owner() are currently only used when
CONFIG_DEBUG_RWSEMS is defined. This causes a compilation error with clang
when `make W=1` and CONFIG_WERROR=y:

kernel/locking/rwsem.c:187:20: error: unused function 'is_rwsem_reader_owned' [-Werror,-Wunused-function]
  187 | static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
      |                    ^~~~~~~~~~~~~~~~~~~~~
kernel/locking/rwsem.c:271:35: error: unused function 'rwsem_owner' [-Werror,-Wunused-function]
  271 | static inline struct task_struct *rwsem_owner(struct rw_semaphore *sem)
      |                                   ^~~~~~~~~~~

Fix this by moving these two functions under the CONFIG_DEBUG_RWSEMS define.
Reported-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20240909182905.161156-1-longman@redhat.com