blob_handler: make commit data parameter optional

Make the commit data parameter optional by defaulting it to an empty
vector.  This is less code than using std::optional for this.

Change-Id: Icd953e63fc68a658b29fff5a132e264f1aee5bbc
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/src/ipmiblob/blob_handler.hpp b/src/ipmiblob/blob_handler.hpp
index 200dfd5..5e24b91 100644
--- a/src/ipmiblob/blob_handler.hpp
+++ b/src/ipmiblob/blob_handler.hpp
@@ -63,7 +63,7 @@
      * @throws BlobException.
      */
     void commit(std::uint16_t session,
-                const std::vector<std::uint8_t>& bytes) override;
+                const std::vector<std::uint8_t>& bytes = {}) override;
 
     /**
      * @throws BlobException.