gfs2: take jdata unstuff into account in do_grow

Before this patch, function do_grow would not reserve enough journal
blocks in the transaction to unstuff jdata files while growing them.
This patch adds the logic to add one more block if the file to grow
is jdata.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Reviewed-by: Andreas Gruenbacher <agruenba@redhat.com>