btrfs: unexport extent_map_block_end()

The helper extent_map_block_end() is currently not used anywhere outside
extent_map.c, so move into from extent_map.h into extent_map.c. While at
it, also make the extent map pointer argument as const.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_map.c

@@ -182,6 +182,13 @@ static struct rb_node *__tree_search(struct rb_root *root, u64 offset,
 	return NULL;
 }
 
+static inline u64 extent_map_block_end(const struct extent_map *em)
+{
+	if (em->block_start + em->block_len < em->block_start)
+		return (u64)-1;
+	return em->block_start + em->block_len;
+}
+
 /* Check to see if two extent_map structs are adjacent and safe to merge. */
 static int mergable_maps(struct extent_map *prev, struct extent_map *next)
 {

fs/btrfs/extent_map.h

@@ -77,13 +77,6 @@ static inline u64 extent_map_end(struct extent_map *em)
 	return em->start + em->len;
 }
 
-static inline u64 extent_map_block_end(struct extent_map *em)
-{
-	if (em->block_start + em->block_len < em->block_start)
-		return (u64)-1;
-	return em->block_start + em->block_len;
-}
-
 void extent_map_tree_init(struct extent_map_tree *tree);
 struct extent_map *lookup_extent_mapping(struct extent_map_tree *tree,
 					 u64 start, u64 len);