lockdep: fix unused function warning in kernel/lockdep.c

Impact: fix build warning

this warning:

  kernel/lockdep.c:584: warning: ‘print_lock_dependencies’ defined but not used

triggers because print_lock_dependencies() is only used if both
CONFIG_TRACE_IRQFLAGS and CONFIG_PROVE_LOCKING are enabled.

But adding #ifdefs is not an option here - it would spread out to 4-5
other helper functions and uglify the file. So mark this function
as __used - it's static and the compiler can eliminate it just fine.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index a428583..c137953 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -580,7 +580,8 @@
 /*
  * printk all lock dependencies starting at <entry>:
  */
-static void print_lock_dependencies(struct lock_class *class, int depth)
+static void __used
+print_lock_dependencies(struct lock_class *class, int depth)
 {
 	struct lock_list *entry;