crypto: starfive - use scatterlist length before DMA mapping

Using sg_dma_len() is only valid after mapping a scatterlist with
dma_map_sg(). However, starfive_aes_aead_do_one_req() uses it before
mapping the scatterlist.

Use the original scatterlist length because the DMA length has not been
populated yet when CONFIG_NEED_SG_DMA_LENGTH=y.

Fixes: 7467147ef9bf ("crypto: starfive - Use dma for aes requests")
Cc: stable@vger.kernel.org
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>