crypto: starfive - Correctly handle return of sg_nents_for_len

crypto: starfive - Correctly handle return of sg_nents_for_len

The return value of sg_nents_for_len was assigned to an unsigned long
in starfive_hash_digest, causing negative error codes to be converted
to large positive integers.

Add error checking for sg_nents_for_len and return immediately on
failure to prevent potential buffer overflows.

Fixes: 7883d1b28a2b ("crypto: starfive - Add hash and HMAC support")
Signed-off-by: Haotian Zhang <vulab@iscas.ac.cn>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>