btrfs: increase ->free_chunk_space in btrfs_grow_device

My overcommit patch exposed a bug with btrfs/177 [1].  The problem here is
that when we grow the device we're not adding to ->free_chunk_space, so
subsequent allocations can cause ->free_chunk_space to wrap, which
causes problems in can_overcommit because we add this to ->total_bytes,
which causes the counter to wrap and gives us an unexpected ENOSPC.

Fix this by properly updating ->free_chunk_space with the new available
space in btrfs_grow_device.

[1] First version of the fix:
    https://lore.kernel.org/linux-btrfs/b97e47ce0ce1d41d221878de7d6090b90aa7a597.1695065233.git.josef@toxicpanda.com/Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -2812,6 +2812,7 @@ int btrfs_grow_device(struct btrfs_trans_handle *trans,
 	btrfs_set_super_total_bytes(super_copy,
 			round_down(old_total + diff, fs_info->sectorsize));
 	device->fs_devices->total_rw_bytes += diff;
+	atomic64_add(diff, &fs_info->free_chunk_space);
 
 	btrfs_device_set_total_bytes(device, new_size);
 	btrfs_device_set_disk_total_bytes(device, new_size);