Avoid 'names_cache' memory leak with CONFIG_AUDITSYSCALL

The nameidata "last.name" is always allocated with "__getname()", and
should always be free'd with "__putname()".

Using "putname()" without the underscores will leak memory, because the
allocation will have been hidden from the AUDITSYSCALL code.

Arguably the real bug is that the AUDITSYSCALL code is really broken,
but in the meantime this fixes the problem people see.

Reported by Robert Derr, patch by Rick Lindsley.

Acked-by: Al Viro <viro@ftp.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>