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: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/arch/s390/crypto/sha_common.c b/arch/s390/crypto/sha_common.c
index f42dbab..48884f8 100644
--- a/arch/s390/crypto/sha_common.c
+++ b/arch/s390/crypto/sha_common.c
@@ -38,6 +38,7 @@
 		BUG_ON(ret != bsize);
 		data += bsize - index;
 		len -= bsize - index;
+		index = 0;
 	}
 
 	/* process as many blocks as possible */