btrfs: remove pointless initialization at btrfs_delayed_refs_rsv_release()

There's no point in initializing to 0 the local variable 'released' as
we don't use it before the next assignment to it. So remove the
initialization. This may help avoid some warnings with clang tools such
as the one reported/fixed by commit 966de47f ("btrfs: remove redundant
initialization of variables in log_new_ancestors").
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/delayed-ref.c

@@ -66,7 +66,7 @@ void btrfs_delayed_refs_rsv_release(struct btrfs_fs_info *fs_info, int nr)
 {
 	struct btrfs_block_rsv *block_rsv = &fs_info->delayed_refs_rsv;
 	const u64 num_bytes = btrfs_calc_delayed_ref_bytes(fs_info, nr);
-	u64 released = 0;
+	u64 released;
 
 	released = btrfs_block_rsv_release(fs_info, block_rsv, num_bytes, NULL);
 	if (released)