lockdep: increase MAX_LOCK_DEPTH

Some code paths exceed the current max lock depth (XFS), so increase
this limit a bit. I looked at making this a dynamic allocated array,
but we should not advocate insane lock depths, so stay with this as
long as it works...
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

include/linux/sched.h

@@ -1189,7 +1189,7 @@ struct task_struct {
 	int softirq_context;
 #endif
 #ifdef CONFIG_LOCKDEP
-# define MAX_LOCK_DEPTH 30UL
+# define MAX_LOCK_DEPTH 48UL
 	u64 curr_chain_key;
 	int lockdep_depth;
 	struct held_lock held_locks[MAX_LOCK_DEPTH];