xfrm: Oops on error in pfkey_msg2xfrm_state()

commit 1e3d0c2c70cd3edb5deed186c5f5c75f2b84a633 upstream.

There are some missing error codes here so we accidentally return NULL
instead of an error pointer.  It results in a NULL pointer dereference.

Fixes: df71837d ("[LSM-IPSec]: Security association restriction.")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>