btrfs: drop get_extent from extent_page_data

Previous patches cleaned up all places where
extent_page_data::get_extent was set and it was btrfs_get_extent all the
time, so we can simply call that instead.

This also reduces size of extent_page_data by 8 bytes which has positive
effect on stack consumption on various functions on the write out path.
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -109,8 +109,6 @@ struct tree_entry {
 struct extent_page_data {
 	struct bio *bio;
 	struct extent_io_tree *tree;
-	get_extent_t *get_extent;
-
 	/* tells writepage not to lock the state bits for this range
 	 * it still does the unlocking
 	 */
@@ -3373,7 +3371,7 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode,
 							 page_end, NULL, 1);
 			break;
 		}
-		em = epd->get_extent(BTRFS_I(inode), page, pg_offset, cur,
+		em = btrfs_get_extent(BTRFS_I(inode), page, pg_offset, cur,
 				     end - cur + 1, 1);
 		if (IS_ERR_OR_NULL(em)) {
 			SetPageError(page);
@@ -4064,7 +4062,6 @@ int extent_write_full_page(struct extent_io_tree *tree, struct page *page,
 	struct extent_page_data epd = {
 		.bio = NULL,
 		.tree = tree,
-		.get_extent = btrfs_get_extent,
 		.extent_locked = 0,
 		.sync_io = wbc->sync_mode == WB_SYNC_ALL,
 	};
@@ -4087,7 +4084,6 @@ int extent_write_locked_range(struct extent_io_tree *tree, struct inode *inode,
 	struct extent_page_data epd = {
 		.bio = NULL,
 		.tree = tree,
-		.get_extent = btrfs_get_extent,
 		.extent_locked = 1,
 		.sync_io = mode == WB_SYNC_ALL,
 	};
@@ -4125,7 +4121,6 @@ int extent_writepages(struct extent_io_tree *tree,
 	struct extent_page_data epd = {
 		.bio = NULL,
 		.tree = tree,
-		.get_extent = btrfs_get_extent,
 		.extent_locked = 0,
 		.sync_io = wbc->sync_mode == WB_SYNC_ALL,
 	};