Fix bug in md5 calculation

Commit 8c432325c3df2075a77b27eab8a87704cf7b48ee introduced a bug for
smaller sizes. Just basically revert the optimization, safer to stay
with a 'reference' implementation than skip a memset.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/verify.c b/verify.c
index 91509e5..6972fe3 100644
--- a/verify.c
+++ b/verify.c
@@ -145,6 +145,7 @@
 		.hash = hash,
 	};
 
+	memset(md5_ctx.hash, 0, sizeof(hdr->md5_digest));
 	md5_update(&md5_ctx, p, hdr->len - sizeof(*hdr));
 
 	if (memcmp(hdr->md5_digest, md5_ctx.hash, sizeof(hash))) {
@@ -236,6 +237,7 @@
 		.hash = (uint32_t *) hdr->md5_digest,
 	};
 
+	memset(md5_ctx.hash, 0, sizeof(hdr->md5_digest));
 	md5_update(&md5_ctx, p, len);
 }