crypto: omap-aes - Fix registration of algorithms

Algorithms can be registered only once. So skip registration of
algorithms if already registered (i.e. in case we have two AES cores
in the system.)

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