shared/helpers.h: fix a typo in a comment

Signed-off-by: Abdur Rehman <arehmanq199@gmail.com>
Reviewed-by: Yong Bakos <ybakos@humanoriented.com>
diff --git a/shared/helpers.h b/shared/helpers.h
index ac9ea8b..46f745d 100644
--- a/shared/helpers.h
+++ b/shared/helpers.h
@@ -64,7 +64,7 @@
 #endif
 
 /**
- * Returns a pointer the the containing struct of a given member item.
+ * Returns a pointer to the containing struct of a given member item.
  *
  * To demonstrate, the following example retrieves a pointer to
  * `example_container` given only its `destroy_listener` member: