apparmor: sparse fix: rename shadowed variables in policy_unpack.c

Fix the following warnings:

security/apparmor/policy_unpack.c:384:35: warning: symbol 'size' shadows an earlier one
security/apparmor/policy_unpack.c:370:24: originally declared here
security/apparmor/policy_unpack.c:443:29: warning: symbol 'tmp' shadows an earlier one
security/apparmor/policy_unpack.c:434:21: originally declared here

Signed-off-by: James Morris <jmorris@namei.org>
Acked-by: John Johansen <john.johansen@canonical.com>