gfs2: Move rs_{sizehint, rgd_gh} fields into the inode

Move the rs_sizehint and rs_rgd_gh fields from struct gfs2_blkreserv
into the inode: they are more closely related to the inode than to a
particular reservation.

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