Fix spelling mistakes using codespell

This commit corrects various spelling mistakes throughout the
repository. The corrections were made automatically using `codespell`[1]
tool.

[1]: https://github.com/codespell-project/codespell

Change-Id: Iccc8a6107616afb3a6b772420651e717a688ce86
Signed-off-by: Manojkiran Eda <manojkiran.eda@gmail.com>
diff --git a/src/callback.hpp b/src/callback.hpp
index 7825faf..0295246 100644
--- a/src/callback.hpp
+++ b/src/callback.hpp
@@ -158,7 +158,7 @@
 };
 
 /** @class ConditionalCallback
- *  @brief Callback adaptor that asssociates a condition with a callback.
+ *  @brief Callback adaptor that associates a condition with a callback.
  */
 template <typename CallbackAccess>
 class ConditionalCallback : public Callback