crypto: sha-s390 - Reset index after processing partial block

The partial block handling in sha-s390 is broken when we get a
partial block that is followed by an update which fills it with
bytes left-over.  Instead of storing the newly left-over bytes
at the start of the buffer, it will be stored immediately after
the previous partial block.

This patch fixes this by resetting the index pointer.
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

arch/s390/crypto/sha_common.c

@@ -38,6 +38,7 @@ int s390_sha_update(struct shash_desc *desc, const u8 *data, unsigned int len)
 		BUG_ON(ret != bsize);
 		data += bsize - index;
 		len -= bsize - index;
+		index = 0;
 	}
 
 	/* process as many blocks as possible */