btrfs: move the mapping_set_error() out of the loop in end_bbio_data_write()

btrfs: move the mapping_set_error() out of the loop in end_bbio_data_write()

Previously we have to call mapping_set_error() inside the
for_each_folio_all() loop, because we do not have a better way to grab
an inode, other than through folio->mapping.

But nowadays every btrfs_bio has its inode member populated, thus we can
easily grab the inode and its i_mapping easily, without the help from a
folio.

Now we can move that mapping_set_error() out of the loop, and use
bbio->inode to grab the i_mapping.

Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>