crypto: atmel-aes - remove useless AES_FLAGS_DMA flag

Since the 'done' task code was split into atmel_aes_cpu_complete() and
atmel_aes_dma_complete(), the AES_FLAGS_DMA flag has become useless.

Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>