crypto: atmel-aes - Fix IV handling when req->nbytes < ivsize

commit 394a9e04 ("crypto: cfb - add missing 'chunksize' property")
adds a test vector where the input length is smaller than the IV length
(the second test vector). This revealed a NULL pointer dereference in
the atmel-aes driver, that is caused by passing an incorrect offset in
scatterwalk_map_and_copy() when atmel_aes_complete() is called.

Do not save the IV in req->info of ablkcipher_request (or equivalently
req->iv of skcipher_request) when req->nbytes < ivsize, because the IV
will not be further used.

While touching the code, modify the type of ivsize from int to
unsigned int, to comply with the return type of
crypto_ablkcipher_ivsize().

Fixes: 91308019

 ("crypto: atmel-aes - properly set IV after {en,de}crypt")
Cc: <stable@vger.kernel.org>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>