Properly initialize md5 hash seed

We started from 0, that's not entirely correct.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/md5.c b/md5.c
index cf1f814..8f9adb2 100644
--- a/md5.c
+++ b/md5.c
@@ -88,6 +88,14 @@
 	hash[3] += d;
 }
 
+void md5_init(struct md5_ctx *mctx)
+{
+	mctx->hash[0] = 0x67452301;
+	mctx->hash[1] = 0xefcdab89;
+	mctx->hash[2] = 0x98badcfe;
+	mctx->hash[3] = 0x10325476;
+}
+
 void md5_update(struct md5_ctx *mctx, const uint8_t *data, unsigned int len)
 {
 	const uint32_t avail = sizeof(mctx->block) - (mctx->byte_count & 0x3f);