GFS2: make sure rgrps are up to date in func gfs2_blk2rgrpd

This patch adds a call to gfs2_rindex_update from function gfs2_blk2rgrpd
and removes calls to it that are made redundant by it. The problem is
that a gfs2_grow can add rgrps to the rindex, then put those rgrps into
use, thus rendering the rindex we read in at mount time incomplete.

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