crypto: omap-aes - Fix CTR mode counter length

NIST vectors for CTR mode in testmgr.h assume the entire IV as the counter. To
get correct results that match the output of these vectors, we need to set the
counter length correctly.

Signed-off-by: Joel Fernandes <joelf@ti.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>