GFS2: Fix quota adjustment return code

This patch changes function gfs2_adjust_quota so that it properly
returns a good (zero) return code on the normal path through the code.
Without this, mounting GFS2 with -o quota=account periodically gave
this error message: GFS2: fsid=cluster:fs: gfs2_quotad: sync error -5

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