btrfs: zoned: return int from btrfs_check_meta_write_pointer

Now that we have writeback_control passed to
btrfs_check_meta_write_pointer(), we can move the wbc condition in
submit_eb_page() to btrfs_check_meta_write_pointer() and return int.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>