selinux: propagate error codes in cond_read_list()

These are passed back when the security module gets loaded.

The original code always returned -1 (-EPERM) on error but after this
patch it can return -EINVAL, or -ENOMEM or propagate the error code from
cond_read_node().  cond_read_node() still returns -1 all the time, but I
fix that in a later patch.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Stephen D. Smalley <sds@tycho.nsa.gov>
Signed-off-by: James Morris <jmorris@namei.org>