motr_sync: [CORTX-33853] Support race coditions during lock acquisition.

Changed lock() implementation to avoid multiple KV operations, thereby
reducing the effect of race during lock() call by caller.

Signed-off-by: Dattaprasad Govekar <dattaprasad.govekar@seagate.com>

src/rgw/motr/sync/motr_sync_impl.cc

@@ -119,12 +119,12 @@ int MotrLock::check_lock(const std::string& lock_name,
         return rc;
       }
     }
-    return -EBUSY;
   } else if (rc == -ENOENT) {
     // Looks like lock object is deleted by another caller
     // as part of the race condition 
     return -EBUSY;
   }
+  return -EBUSY;
 }
 
 int MotrKVLockProvider::read_lock(const std::string& lock_name,