Fix kzalloc() and kstrdup() caller report for CONFIG_DEBUG_SLAB.  We must
pass the caller to __cache_alloc() instead of directly doing
__builtin_return_address(0) there; otherwise kzalloc() and kstrdup() are
reported as the allocation site instead of the real one.

Thanks to Valdis Kletnieks for reporting the problem and Steven Rostedt for
the original idea.
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>