fix more leaks in audit_tree.c tag_chunk()

Several leaks in audit_tree didn't get caught by commit
318b6d3d

, including the leak on normal
exit in case of multiple rules refering to the same chunk.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>