selinux: drop unnecessary smp_load_acquire() call

In commit 66f8e2f0 ("selinux: sidtab reverse lookup hash table") the
corresponding load is moved under the spin lock, so there is no race
possible and we can read the count directly. The smp_store_release() is
still needed to avoid racing with the lock-free readers.

Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>