arch/sh/kernel/dwarf.c: use rbtree postorder iteration helper instead of solution...

arch/sh/kernel/dwarf.c: use rbtree postorder iteration helper instead of solution using repeated rb_erase()

Use rbtree_postorder_for_each_entry_safe() to destroy the rbtree instead
of using repeated rb_erase() calls

Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>