selinux: fix error codes in cond_policydb_init()

It's better to propagate the error code from avtab_init() instead of
returning -1 (-EPERM).  It turns out that avtab_init() never fails so
this patch doesn't change how the code runs but it's still a clean up.

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>