crypto: omap-aes - prevent unregistering algorithms twice

Most of the OMAP family SoCs contain two instances for AES core, which
causes the remove callbacks to be also done twice when driver is
removed. Fix the algorithm unregister callbacks to take into account the
number of algorithms still registered to avoid removing these twice.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>