btrfs: sink get_extent parameter to extent_writepages

There's only one caller.
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -4121,14 +4121,13 @@ int extent_write_locked_range(struct extent_io_tree *tree, struct inode *inode,
 
 int extent_writepages(struct extent_io_tree *tree,
 		      struct address_space *mapping,
-		      get_extent_t *get_extent,
 		      struct writeback_control *wbc)
 {
 	int ret = 0;
 	struct extent_page_data epd = {
 		.bio = NULL,
 		.tree = tree,
-		.get_extent = get_extent,
+		.get_extent = btrfs_get_extent,
 		.extent_locked = 0,
 		.sync_io = wbc->sync_mode == WB_SYNC_ALL,
 	};

fs/btrfs/extent_io.h

@@ -411,7 +411,6 @@ int extent_write_locked_range(struct extent_io_tree *tree, struct inode *inode,
 			      int mode);
 int extent_writepages(struct extent_io_tree *tree,
 		      struct address_space *mapping,
-		      get_extent_t *get_extent,
 		      struct writeback_control *wbc);
 int btree_write_cache_pages(struct address_space *mapping,
 			    struct writeback_control *wbc);

fs/btrfs/inode.c

@@ -8903,7 +8903,7 @@ static int btrfs_writepages(struct address_space *mapping,
 	struct extent_io_tree *tree;
 
 	tree = &BTRFS_I(mapping->host)->io_tree;
-	return extent_writepages(tree, mapping, btrfs_get_extent, wbc);
+	return extent_writepages(tree, mapping, wbc);
 }
 
 static int