crypto: rockchip - Fix dma_unmap_sg() nents value

The dma_unmap_sg() functions should be called with the same nents as the
dma_map_sg(), not the value the map function returned.

Fixes: 57d67c6e ("crypto: rockchip - rework by using crypto_engine")
Cc: <stable@vger.kernel.org>
Signed-off-by: Thomas Fourier <fourier.thomas@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>