crypto: omap-aes - Convert kzalloc to devm_kzalloc

Use devm_kzalloc instead of kzalloc. With this change, there is no need to
call kfree in error/exit paths.

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