Fix HSET response decoding

The command internally uses (the deprecated) HMSET which just returns OK
on success instead of the amount of fields written

Signed-off-by: Lee Smet <lee.smet@hotmail.com>

src/storage/redis.rs

@@ -122,7 +122,7 @@ impl RedisDriver {
             warn!(db=%db, key=%key, error=%e, "DEL before HSET failed");
         }
         // Write all fields
-        let _: usize = cm.hset_multiple(key, &pairs).await.map_err(|e| {
+        let _: () = cm.hset_multiple(key, &pairs).await.map_err(|e| {
             error!(db=%db, key=%key, error=%e, "HSET multiple failed");
             e
         })?;