crypto: atmel-ecc - fix to allow multi segment scatterlists

Remove the limitation of single element scatterlists. ECDH with
multi-element scatterlists is needed by TPM.

Similar to 'commit 95ec01ba ("crypto: ecdh - fix to allow multi
segment scatterlists")'.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>