GFS2: Ensure that the inode goal block settings are updated

GFS2: Ensure that the inode goal block settings are updated

GFS2 has a goal block associated with each inode indicating the
search start position for future block allocations (in fact there
are two, but thats for backward compatibility with GFS1 as they
are set to identical locations in GFS2).

In some circumstances, depending on the ordering of updates to
the inode it was possible for the goal block settings to not
be updated on disk. This patch ensures that the goal block will
always get updated, thus reducing the potential for searching
the same (already allocated) blocks again when looking for free
space during block allocation.

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