commonlib/list: Drop 'const' qualifier from return type

The 'const' qualifier is unnecessary for the return values of the
following:

- list_next()
- list_prev()
- list_first()
- list_last()

Therefore, drop it. No caller needs to be changed.

Change-Id: I0f5bc2b0ed3cd47d0d6355c8dffea17f6e085407
Signed-off-by: Yu-Ping Wu <yupingso@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/91113
Reviewed-by: Jakub "Kuba" Czapiga <czapiga@google.com>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/commonlib/include/commonlib/list.h

@@ -29,27 +29,27 @@ static inline bool list_is_empty(const struct list_node *head)
 }
 
 // Get next node.
-static inline const struct list_node *list_next(const struct list_node *node,
-						const struct list_node *head)
+static inline struct list_node *list_next(const struct list_node *node,
+					  const struct list_node *head)
 {
 	return node->next;
 };
 
 // Get prev node.
-static inline const struct list_node *list_prev(const struct list_node *node,
-						const struct list_node *head)
+static inline struct list_node *list_prev(const struct list_node *node,
+					  const struct list_node *head)
 {
 	return node->prev == head ? NULL : node->prev;
 };
 
 // Get first node.
-static inline const struct list_node *list_first(const struct list_node *head)
+static inline struct list_node *list_first(const struct list_node *head)
 {
 	return list_is_empty(head) ? NULL : head->next;
 }
 
 // Get last node.
-const struct list_node *list_last(const struct list_node *head);
+struct list_node *list_last(const struct list_node *head);
 
 // Get the number of list elements.
 size_t list_length(const struct list_node *head);

src/commonlib/list.c

@@ -37,12 +37,15 @@ void list_append(struct list_node *node, struct list_node *head)
 	list_insert_after(node, head);
 }
 
-const struct list_node *list_last(const struct list_node *head)
+struct list_node *list_last(const struct list_node *head)
 {
-	const struct list_node *ptr = head;
+	if (!head->next)
+		return NULL;
+
+	struct list_node *ptr = head->next;
 	while (ptr->next)
 		ptr = ptr->next;
-	return ptr == head ? NULL : ptr;
+	return ptr;
 }
 
 size_t list_length(const struct list_node *head)