btrfs: Remove unused variable

Src was initially part of 31ff1cd25d ("Btrfs: Copy into the log tree in
big batches"), however 16e7549f04 ("Btrfs: incompatible format change
to remove hole extents") changed parameters passed to copy_items which
made the src variable redundant.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Timofey Titovets <nefelim4ag@gmail.com>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/tree-log.c

@@ -4647,7 +4647,6 @@ static int btrfs_log_inode(struct btrfs_trans_handle *trans,
 	struct btrfs_key min_key;
 	struct btrfs_key max_key;
 	struct btrfs_root *log = root->log_root;
-	struct extent_buffer *src = NULL;
 	LIST_HEAD(logged_list);
 	u64 last_extent = 0;
 	int err = 0;
@@ -4890,7 +4889,6 @@ again:
 			goto next_slot;
 		}
 
-		src = path->nodes[0];
 		if (ins_nr && ins_start_slot + ins_nr == path->slots[0]) {
 			ins_nr++;
 			goto next_slot;