KEYS: Do preallocation for __key_link()

Do preallocation for __key_link() so that the various callers in request_key.c
can deal with any errors from this source before attempting to construct a key.
This allows them to assume that the actual linkage step is guaranteed to be
successful.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>

diff --cc security/keys/internal.h
Simple merge

diff --cc security/keys/key.c
Simple merge

diff --cc security/keys/keyring.c
Simple merge

diff --cc security/keys/request_key.c
Simple merge