Don't unnecessarily use named returns

They get horribly confusing, especially here where we use "rc"
for two completely different purposes:
containers/podman#22575 (comment)

Should not change behavior.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

storage/storage_src.go

@@ -107,12 +107,11 @@ func (s *storageImageSource) Close() error {
 // GetBlob returns a stream for the specified blob, and the blob’s size (or -1 if unknown).
 // The Digest field in BlobInfo is guaranteed to be provided, Size may be -1 and MediaType may be optionally provided.
 // May update BlobInfoCache, preferably after it knows for certain that a blob truly exists at a specific location.
-func (s *storageImageSource) GetBlob(ctx context.Context, info types.BlobInfo, cache types.BlobInfoCache) (rc io.ReadCloser, n int64, err error) {
+func (s *storageImageSource) GetBlob(ctx context.Context, info types.BlobInfo, cache types.BlobInfoCache) (io.ReadCloser, int64, error) {
 	// We need a valid digest value.
 	digest := info.Digest
 
-	err = digest.Validate()
-	if err != nil {
+	if err := digest.Validate(); err != nil {
 		return nil, 0, err
 	}
 
@@ -154,7 +153,7 @@ func (s *storageImageSource) GetBlob(ctx context.Context, info types.BlobInfo, c
 	// NOTE: the blob is first written to a temporary file and subsequently
 	// closed.  The intention is to keep the time we own the storage lock
 	// as short as possible to allow other processes to access the storage.
-	rc, n, _, err = s.getBlobAndLayerID(digest, layers)
+	rc, n, _, err := s.getBlobAndLayerID(digest, layers)
 	if err != nil {
 		return nil, 0, err
 	}