bloblist: Zero records when adding

It is convenient for bloblist to zero out the contents of a records when
it is added. This saves the callers having to do it.

Update the API accordingly.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/README.bloblist b/doc/README.bloblist
index b0e787b..274c460 100644
--- a/doc/README.bloblist
+++ b/doc/README.bloblist
@@ -55,8 +55,8 @@
 API
 ---
 
-Bloblist provides a fairly simple API which allows blobs to be created  and
-found. All access is via the blob's tag.
+Bloblist provides a fairly simple API which allows blobs to be created and
+found. All access is via the blob's tag. Blob records are zeroed when added.
 
 
 Finishing the bloblist