[PATCH] key: plug request_key_auth memleak

Plug request_key_auth memleak.  This can be triggered by unprivileged
users, so is local DoS.

Signed-off-by: Chris Wright <chrisw@osdl.org>
Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>