crypto: sun4i-ss - linearize buffers content must be kept

When running the non-optimized cipher function, SS produce partial random
output.
This is due to linearize buffers being reseted after each loop.

For preserving stack, instead of moving them back to start of function,
I move them in sun4i_ss_ctx.

Fixes: 8d3bcb99 ("crypto: sun4i-ss - reduce stack usage")
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>