ocfs2: Reserve 1 more cluster in expanding_inline_dir for indexed dir.

In ocfs2_expand_inline_dir, we calculate whether we need 1 extra
cluster if we can't store the dx inline the root and save it in
dx_alloc. So add it when we call ocfs2_reserve_clusters.

Signed-off-by: Tao Ma <tao.ma@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>